If you're running the RTR AE servo, it may well be worn out or weak. So keep that in mind that it is likely a good idea to get a nicer servo.

Also, the servo saver, located just to the front of the servo on the right side of the vehicle (refer to your instruction manual) consists of a sprung hub/ramp assembly. They're known for being a little weak, so when the servo actuates against the tires, it ramps up instead. It is there to "save the servo" when you hit a wall. So it is safer to run with it.

But, some of us prefer to put glue on the ramp surfaces in order to lock it out. This is also part of why you see AE and JConcepts/Avid with the aluminum steering bellcranks now.

Your servo horn may also be stripped/worn, so check it against the servo splines as well.