diff --git a/.gitignore b/.gitignore
index 4ddb12b..44f5741 100644
--- a/.gitignore
+++ b/.gitignore
@@ -34,6 +34,7 @@ ipython_config.py
 # Environments
 .env
 .venv
+.python-version
 env/
 venv/
 ENV/
@@ -69,6 +70,7 @@ requirements.dev.txt
 manuscript.pdf
 /data/rpgn_example/
 /rpgn/
+/benchmark/
 
 # All .DS_Store files
 **/.DS_Store
diff --git a/.python-version b/.python-version
deleted file mode 100644
index 2c07333..0000000
--- a/.python-version
+++ /dev/null
@@ -1 +0,0 @@
-3.11
diff --git a/pyproject.toml b/pyproject.toml
index 61c8f11..6e94180 100755
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -58,7 +58,6 @@ dev = [
     "pandas-stubs",
     "pandoc",
     "pre-commit",
-    "pybiomart",
     "pytest",
     "sphinx",
     "sphinx-autoapi",
@@ -66,7 +65,6 @@ dev = [
     "sphinx-copybutton",
     "sphinx-design",
     "sphinx-rtd-theme",
-    "virtualenv",
 ]
 
 [project.scripts]
diff --git a/pytximport/core/_tximport.py b/pytximport/core/_tximport.py
index 1b0e807..8436e9d 100644
--- a/pytximport/core/_tximport.py
+++ b/pytximport/core/_tximport.py
@@ -141,10 +141,14 @@ def tximport(
             raise FileNotFoundError(f"The transcript to gene mapping does not exist: {transcript_gene_map}")
 
         try:
-            if transcript_gene_map.suffix == ".csv":
-                transcript_gene_map = pd.read_csv(transcript_gene_map, header=0, engine="pyarrow")
-            else:
-                transcript_gene_map = pd.read_table(transcript_gene_map, header=0, engine="pyarrow")
+            transcript_gene_map = pd.read_csv(
+                transcript_gene_map,
+                header=0,
+                engine="pyarrow",
+                sep=("," if transcript_gene_map.suffix == ".csv" else "\t"),
+                usecols=["transcript_id", "gene_id"],
+                dtype={"transcript_id": str, "gene_id": str},
+            )
         except Exception as exception:
             raise ValueError(f"Could not read the transcript to gene mapping: {exception}")
 
@@ -445,6 +449,7 @@ def tximport(
                 if transcript_gene_map is None:
                     raise ValueError("A transcript to gene mapping must be provided for `dtu_scaled_tpm`.")
 
+                log(25, "Calculating median gene length over isoforms.")
                 transcript_data = get_median_length_over_isoform(
                     transcript_data,
                     transcript_gene_map,
diff --git a/pytximport/importers/_read_kallisto.py b/pytximport/importers/_read_kallisto.py
index 4f90b53..97574f1 100644
--- a/pytximport/importers/_read_kallisto.py
+++ b/pytximport/importers/_read_kallisto.py
@@ -3,7 +3,6 @@
 from typing import Optional, Union
 
 import numpy as np
-import pandas as pd
 from h5py import File
 
 from ..definitions import InferentialReplicates, TranscriptData
diff --git a/pytximport/importers/_read_tsv.py b/pytximport/importers/_read_tsv.py
index b5c9c41..b0e6968 100644
--- a/pytximport/importers/_read_tsv.py
+++ b/pytximport/importers/_read_tsv.py
@@ -84,25 +84,23 @@ def read_tsv(
     if not file_path.exists():
         raise ImportError(f"The file does not exist: {file_path}")
 
-    # Read the quantification file as a tsv, tab separated and the first line is the column names
-    if file_path.suffix == ".gz":
-        transcript_dataframe = pd.read_table(file_path, header=0, compression="gzip", sep="\t")
-    else:
-        usecols = [id_column, counts_column, length_column]
-        dtype = {id_column: str, counts_column: np.float64, length_column: np.float64}
-
-        if abundance_column is not None:
-            usecols.append(abundance_column)
-            dtype[abundance_column] = np.float64
-
-        transcript_dataframe = pd.read_table(
-            file_path,
-            header=0,
-            sep="\t",
-            engine="pyarrow",
-            usecols=usecols,
-            dtype=dtype,
-        )
+    # Read the quantification file as a tsv, tab separated with the first line being the column names
+    usecols = [id_column, counts_column, length_column]
+    dtype = {id_column: str, counts_column: np.float64, length_column: np.float64}
+
+    if abundance_column is not None:
+        usecols.append(abundance_column)
+        dtype[abundance_column] = np.float64
+
+    transcript_dataframe = pd.read_table(
+        file_path,
+        header=0,
+        sep="\t",
+        compression=("gzip" if file_path.suffix == ".gz" else None),
+        engine="pyarrow",
+        usecols=usecols,
+        dtype=dtype,
+    )
 
     return parse_dataframe(
         transcript_dataframe,
diff --git a/pytximport/utils/_convert_abundance_to_counts.py b/pytximport/utils/_convert_abundance_to_counts.py
index 5339a89..3390319 100644
--- a/pytximport/utils/_convert_abundance_to_counts.py
+++ b/pytximport/utils/_convert_abundance_to_counts.py
@@ -33,9 +33,6 @@ def convert_abundance_to_counts(
         raise ValueError("The count transform must be 'scaled_tpm' or 'length_scaled_tpm'.")
 
     # Scale the counts from abundance to the original sequencing depth of each sample
-    column_counts = counts.sum(axis=0)
-    new_counts = counts_transformed.sum(axis=0)
-    ratio = column_counts / new_counts
-    counts_transformed = (counts_transformed.T * ratio).T
+    counts_transformed = (counts_transformed.T * (counts.sum(axis=0) / counts_transformed.sum(axis=0))).T
 
     return counts_transformed
diff --git a/pytximport/utils/_convert_counts_to_tpm.py b/pytximport/utils/_convert_counts_to_tpm.py
index 9cde9e7..25b963d 100644
--- a/pytximport/utils/_convert_counts_to_tpm.py
+++ b/pytximport/utils/_convert_counts_to_tpm.py
@@ -14,5 +14,4 @@ def convert_counts_to_tpm(
     Returns:
         np.ndarray: The transcript-level expression data with the TPM.
     """
-    normalization_factor = 1e6 / np.sum(counts / length)
-    return np.array(counts * normalization_factor / length)
+    return np.array(counts * (1e6 / np.sum(counts / length)) / length)
diff --git a/pytximport/utils/_convert_transcripts_to_genes.py b/pytximport/utils/_convert_transcripts_to_genes.py
index 925bf27..e54a5d8 100644
--- a/pytximport/utils/_convert_transcripts_to_genes.py
+++ b/pytximport/utils/_convert_transcripts_to_genes.py
@@ -35,7 +35,6 @@ def convert_transcripts_to_genes(
         xr.Dataset: The gene-level expression data from multiple samples.
     """
     transcript_ids: Union[np.ndarray, List[str]] = transcript_data.coords["transcript_id"].values
-    transcript_ids = transcript_data.coords["transcript_id"].values
 
     if ignore_after_bar:
         # Ignore the part of the transcript ID after the bar
@@ -72,19 +71,21 @@ def convert_transcripts_to_genes(
         )
         # Remove the missing transcripts by only keeping the data for the transcripts present in the mapping
         transcript_ids_intersect = list(set(unique_transcripts).intersection(set(transcript_gene_map["transcript_id"])))
-        transcript_ids_intersect_boolean = np.isin(transcript_ids, transcript_ids_intersect)
         transcript_data = transcript_data.isel(
-            transcript_id=transcript_ids_intersect_boolean,
+            transcript_id=np.isin(transcript_ids, transcript_ids_intersect),
             drop=True,
         )
-        transcript_ids = transcript_data.coords["transcript_id"].values
+        # transcript_ids = transcript_data.coords["transcript_id"].values
         transcript_gene_map = transcript_gene_map[transcript_gene_map["transcript_id"].isin(transcript_ids_intersect)]
 
     # Add the corresponding gene to the transcript-level expression
     log(25, "Matching gene_ids.")
-    transcript_gene_dict = transcript_gene_map.set_index("transcript_id")["gene_id"].to_dict()
-    gene_ids_raw = transcript_data["transcript_id"].to_series().map(transcript_gene_dict).values
-    # gene_ids = np.repeat(gene_ids_raw, transcript_data["abundance"].shape[1])  # type: ignore
+    gene_ids_raw = (
+        transcript_data["transcript_id"]
+        .to_series()
+        .map(transcript_gene_map.set_index("transcript_id")["gene_id"])
+        .values
+    )
 
     # Remove the transcript_id coordinate and rename the variable to gene_id
     transcript_data = (
diff --git a/pytximport/utils/_create_transcript_gene_map.py b/pytximport/utils/_create_transcript_gene_map.py
index 97fa8bd..b2ad96d 100644
--- a/pytximport/utils/_create_transcript_gene_map.py
+++ b/pytximport/utils/_create_transcript_gene_map.py
@@ -101,7 +101,7 @@ def create_transcript_gene_map_from_annotation(
         # Each attribute line looks like this:
         # gene_id ""; transcript_id ""; gene_name ""; gene_source ""; gene_biotype "";
         # transcript_name ""; transcript_source "";
-        # We are only interested in the gene_id, gene_name, and transcript_id
+        # We are only interested in the gene_id, gene_name, transcript_id, transcript_name and gene_biotype
         attribute_columns = [
             "transcript_id",
             "transcript_name",
diff --git a/pytximport/utils/_get_median_length_over_isoform.py b/pytximport/utils/_get_median_length_over_isoform.py
index 12f725a..b063dd9 100644
--- a/pytximport/utils/_get_median_length_over_isoform.py
+++ b/pytximport/utils/_get_median_length_over_isoform.py
@@ -22,31 +22,35 @@ def get_median_length_over_isoform(
     assert "length" in transcript_data.data_vars, "The transcript data does not contain a `length` variable."
 
     # Get the gene ids for each transcript
-    transcript_gene_dict = transcript_gene_map.set_index("transcript_id")["gene_id"].to_dict()
-    gene_ids = transcript_data["transcript_id"].to_series().map(transcript_gene_dict).values
+    gene_ids = (
+        transcript_data["transcript_id"]
+        .to_series()
+        .map(transcript_gene_map.set_index("transcript_id")["gene_id"].to_dict())
+        .values
+    )
 
     # Check that no gene ids is nan
     assert not any(pd.isna(gene_ids)), "Not all transcript ids could be mapped to gene ids. Please check the mapping."
 
-    transcript_data_copy = transcript_data.drop_vars("transcript_id")
-    transcript_data_copy = transcript_data_copy.assign_coords(gene_id=gene_ids)
-    transcript_data_copy = transcript_data_copy.rename({"transcript_id": "gene_id"})
-
     # Get the row mean across samples for each transcript
-    average_transcript_length_across_samples = transcript_data_copy["length"].mean(axis=1)
-    median_gene_length = average_transcript_length_across_samples.groupby("gene_id").median().to_dataframe()
-
-    transcript_median_gene_length = [median_gene_length.loc[gene_id, "length"] for gene_id in gene_ids]
-    transcript_median_gene_length_repeated = np.reshape(
-        np.repeat(
-            transcript_median_gene_length,
-            transcript_data["abundance"].shape[1],
-        ),
-        transcript_data["abundance"].shape,
+    median_gene_length = (
+        transcript_data.drop_vars("transcript_id")
+        .assign_coords(gene_id=gene_ids)
+        .rename({"transcript_id": "gene_id"})["length"]
+        .mean(dim="file")
+        .groupby("gene_id")
+        .median()
+        .to_dataframe()
     )
 
     transcript_data["median_isoform_length"] = xr.DataArray(
-        transcript_median_gene_length_repeated,
+        np.reshape(
+            np.repeat(
+                pd.Series(gene_ids).map(median_gene_length["length"]).to_numpy(),
+                transcript_data["abundance"].shape[1],
+            ),
+            transcript_data["abundance"].shape,
+        ),
         dims=("transcript_id", "file"),
     )
 
diff --git a/pytximport/utils/_replace_transcript_ids_with_names.py b/pytximport/utils/_replace_transcript_ids_with_names.py
index c34756a..2215f77 100644
--- a/pytximport/utils/_replace_transcript_ids_with_names.py
+++ b/pytximport/utils/_replace_transcript_ids_with_names.py
@@ -24,7 +24,13 @@ def replace_transcript_ids_with_names(
     """
     # Read the transcript to gene mapping
     if isinstance(transcript_name_map, str) or isinstance(transcript_name_map, Path):
-        transcript_name_map = pd.read_table(transcript_name_map, header=0)
+        transcript_name_map = pd.read_table(
+            transcript_name_map,
+            header=0,
+            engine="c",
+            usecols=["transcript_id", "transcript_name"],
+            dtype=str,
+        )
         transcript_name_map = transcript_name_map.drop_duplicates()
 
     # Check that transcript_id and transcript_name are present in the mapping