There is a TC5 thread where car-specific topics are discussed. I assume your "twitchy" issue was handling related and not radio interference, but post more of your setup including shock, tire and track details and we should be able to troubleshoot.
You can also go to www.rc10.com
, click on the Support tab, then choose Setups and finally TC5. If you match the track surface to where you run, the setup should get you fairly close to optimal. Remember to put the ENTIRE setup on the car, and make sure all moving pieces are not binding (arms, hubs, steering, shocks, etc.)