If your truck doesn't have ball bearings, that is absolutely #1 - especially the tranny. Removing the carb restrictor will tear up a bushing-filled tranny in a heartbeat! #2 is the servos as suggested by others. #3 may be the rear a-arm mounts and the bulkhead. These are weak links in a tumble. From that point, any other aftermarket parts are mostly for serious racers. These parts usually lighten the car, or increase performance by small percentages. Other than Tower, you might try ehobbies.com or acehardwarehobbies.com. I use ebay a lot, but strongly caution newbies.