diff --git a/codeflash/code_utils/instrument_existing_tests.py b/codeflash/code_utils/instrument_existing_tests.py
index db08f8afc..f34a72f81 100644
--- a/codeflash/code_utils/instrument_existing_tests.py
+++ b/codeflash/code_utils/instrument_existing_tests.py
@@ -351,29 +351,40 @@ def visit_FunctionDef(self, node: ast.FunctionDef) -> ast.FunctionDef:
     def _process_test_function(
         self, node: ast.AsyncFunctionDef | ast.FunctionDef
     ) -> ast.AsyncFunctionDef | ast.FunctionDef:
-        if self.test_framework == "unittest" and not any(
-            isinstance(d, ast.Call) and isinstance(d.func, ast.Name) and d.func.id == "timeout_decorator.timeout"
-            for d in node.decorator_list
-        ):
-            timeout_decorator = ast.Call(
-                func=ast.Name(id="timeout_decorator.timeout", ctx=ast.Load()),
-                args=[ast.Constant(value=15)],
-                keywords=[],
-            )
-            node.decorator_list.append(timeout_decorator)
+        # Cache the test_framework check and decorator_list reference for better performance
+        if self.test_framework == "unittest":
+            decorlist = node.decorator_list
+            # Use a generator expression with a break sentinel for efficiency
+            timeout_found = False
+            for d in decorlist:
+                if (
+                    isinstance(d, ast.Call)
+                    and isinstance(d.func, ast.Name)
+                    and d.func.id == "timeout_decorator.timeout"
+                ):
+                    timeout_found = True
+                    break
+            if not timeout_found:
+                timeout_decorator = ast.Call(
+                    func=ast.Name(id="timeout_decorator.timeout", ctx=ast.Load()),
+                    args=[ast.Constant(value=15)],
+                    keywords=[],
+                )
+                decorlist.append(timeout_decorator)
 
         # Initialize counter for this test function
         if node.name not in self.async_call_counter:
             self.async_call_counter[node.name] = 0
 
         new_body = []
+        async_call_counter = self.async_call_counter  # Local binding for minor speedup
 
         for _i, stmt in enumerate(node.body):
             transformed_stmt, added_env_assignment = self._instrument_statement(stmt, node.name)
 
             if added_env_assignment:
-                current_call_index = self.async_call_counter[node.name]
-                self.async_call_counter[node.name] += 1
+                current_call_index = async_call_counter[node.name]
+                async_call_counter[node.name] += 1
 
                 env_assignment = ast.Assign(
                     targets=[
@@ -386,7 +397,7 @@ def _process_test_function(
                         )
                     ],
                     value=ast.Constant(value=f"{current_call_index}"),
-                    lineno=stmt.lineno if hasattr(stmt, "lineno") else 1,
+                    lineno=getattr(stmt, "lineno", 1),  # More efficient than hasattr
                 )
                 new_body.append(env_assignment)
                 self.did_instrument = True
@@ -397,16 +408,20 @@ def _process_test_function(
         return node
 
     def _instrument_statement(self, stmt: ast.stmt, _node_name: str) -> tuple[ast.stmt, bool]:
-        for node in ast.walk(stmt):
+        # Instead of ast.walk, use a manual stack to avoid unnecessary generator overhead
+        stack = [stmt]
+        while stack:
+            node = stack.pop()
             if (
                 isinstance(node, ast.Await)
                 and isinstance(node.value, ast.Call)
                 and self._is_target_call(node.value)
                 and self._call_in_positions(node.value)
             ):
-                # Check if this call is in one of our target positions
-                return stmt, True  # Return original statement but signal we added env var
-
+                return stmt, True
+            # Instead of ast.walk's recursive generator, use direct child iteration
+            for child in ast.iter_child_nodes(node):
+                stack.append(child)
         return stmt, False
 
     def _is_target_call(self, call_node: ast.Call) -> bool: