Not sure about the problem being caused by a warped chassis, but you may want to consider the following:
* Swap the steering and throttle servo
* Completely disassemble and reassemble the car. Yes, it's a major pain, but you may find something you were not expecting. When I recently disassembled my car, I found out that one of my bearings had seized and another one was starting to go bad. In addition, once you've stripped down the chassis, you can make sure it's okay.
Just some ideas. Hope it helps.