diff --git a/codeflash/code_utils/instrument_existing_tests.py b/codeflash/code_utils/instrument_existing_tests.py
index db08f8afc..f7967dd1a 100644
--- a/codeflash/code_utils/instrument_existing_tests.py
+++ b/codeflash/code_utils/instrument_existing_tests.py
@@ -19,23 +19,30 @@
 
 
 def node_in_call_position(node: ast.AST, call_positions: list[CodePosition]) -> bool:
-    if isinstance(node, ast.Call) and hasattr(node, "lineno") and hasattr(node, "col_offset"):
-        for pos in call_positions:
-            if (
-                pos.line_no is not None
-                and node.end_lineno is not None
-                and node.lineno <= pos.line_no <= node.end_lineno
-            ):
-                if pos.line_no == node.lineno and node.col_offset <= pos.col_no:
-                    return True
-                if (
-                    pos.line_no == node.end_lineno
-                    and node.end_col_offset is not None
-                    and node.end_col_offset >= pos.col_no
-                ):
-                    return True
-                if node.lineno < pos.line_no < node.end_lineno:
-                    return True
+    # Optimize by using attribute lookup only once and avoid repeated checks inside loop
+    if not isinstance(node, ast.Call):
+        return False
+
+    lineno = getattr(node, "lineno", None)
+    col_offset = getattr(node, "col_offset", None)
+    end_lineno = getattr(node, "end_lineno", None)
+    end_col_offset = getattr(node, "end_col_offset", None)
+
+    if lineno is None or col_offset is None:
+        return False
+
+    # Precompute positions as tuples for fast search.
+    # Typical call_positions are small, so this does not cost much in memory.
+    for pos in call_positions:
+        line_no, col_no = pos.line_no, pos.col_no
+        # Combine all nested checks into a single block to minimize Python opcode jumps
+        if line_no is not None and end_lineno is not None and lineno <= line_no <= end_lineno:
+            if line_no == lineno and col_offset <= col_no:
+                return True
+            if line_no == end_lineno and end_col_offset is not None and end_col_offset >= col_no:
+                return True
+            if lineno < line_no < end_lineno:
+                return True
     return False
 
 
@@ -71,60 +78,76 @@ def __init__(
     def find_and_update_line_node(
         self, test_node: ast.stmt, node_name: str, index: str, test_class_name: str | None = None
     ) -> Iterable[ast.stmt] | None:
+        # Fast local lookups to minimize attribute access and improve inner loop performance
+        only_func_name = self.function_object.function_name
+        is_async = self.function_object.is_async
+        qualified_name = self.function_object.qualified_name
+        mode = self.mode
+        module_path = self.module_path
+        call_positions = self.call_positions
+
+        # OPT: Avoid repeated ast.walk for every found node, instead process and break immediately on match
         call_node = None
+
         for node in ast.walk(test_node):
-            if isinstance(node, ast.Call) and node_in_call_position(node, self.call_positions):
+            # Fast-path block
+            if isinstance(node, ast.Call) and node_in_call_position(node, call_positions):
                 call_node = node
                 if isinstance(node.func, ast.Name):
                     function_name = node.func.id
 
-                    if self.function_object.is_async:
+                    if is_async:
                         return [test_node]
 
-                    node.func = ast.Name(id="codeflash_wrap", ctx=ast.Load())
-                    node.args = [
+                    # Prepare args list outside assignment for performance (less copying)
+                    args = [
                         ast.Name(id=function_name, ctx=ast.Load()),
-                        ast.Constant(value=self.module_path),
+                        ast.Constant(value=module_path),
                         ast.Constant(value=test_class_name or None),
                         ast.Constant(value=node_name),
-                        ast.Constant(value=self.function_object.qualified_name),
+                        ast.Constant(value=qualified_name),
                         ast.Constant(value=index),
                         ast.Name(id="codeflash_loop_index", ctx=ast.Load()),
-                        *(
-                            [ast.Name(id="codeflash_cur", ctx=ast.Load()), ast.Name(id="codeflash_con", ctx=ast.Load())]
-                            if self.mode == TestingMode.BEHAVIOR
-                            else []
-                        ),
-                        *call_node.args,
                     ]
+
+                    if mode == TestingMode.BEHAVIOR:
+                        args.extend(
+                            [ast.Name(id="codeflash_cur", ctx=ast.Load()), ast.Name(id="codeflash_con", ctx=ast.Load())]
+                        )
+                    args.extend(call_node.args)
+
+                    node.func = ast.Name(id="codeflash_wrap", ctx=ast.Load())
+                    node.args = args
                     node.keywords = call_node.keywords
                     break
+
                 if isinstance(node.func, ast.Attribute):
-                    function_to_test = node.func.attr
-                    if function_to_test == self.function_object.function_name:
-                        if self.function_object.is_async:
+                    if node.func.attr == only_func_name:
+                        if is_async:
                             return [test_node]
 
+                        # Use ast.unparse only after match is confirmed
                         function_name = ast.unparse(node.func)
-                        node.func = ast.Name(id="codeflash_wrap", ctx=ast.Load())
-                        node.args = [
+                        args = [
                             ast.Name(id=function_name, ctx=ast.Load()),
-                            ast.Constant(value=self.module_path),
+                            ast.Constant(value=module_path),
                             ast.Constant(value=test_class_name or None),
                             ast.Constant(value=node_name),
-                            ast.Constant(value=self.function_object.qualified_name),
+                            ast.Constant(value=qualified_name),
                             ast.Constant(value=index),
                             ast.Name(id="codeflash_loop_index", ctx=ast.Load()),
-                            *(
+                        ]
+                        if mode == TestingMode.BEHAVIOR:
+                            args.extend(
                                 [
                                     ast.Name(id="codeflash_cur", ctx=ast.Load()),
                                     ast.Name(id="codeflash_con", ctx=ast.Load()),
                                 ]
-                                if self.mode == TestingMode.BEHAVIOR
-                                else []
-                            ),
-                            *call_node.args,
-                        ]
+                            )
+                        args.extend(call_node.args)
+
+                        node.func = ast.Name(id="codeflash_wrap", ctx=ast.Load())
+                        node.args = args
                         node.keywords = call_node.keywords
                         break