So at certain distances, approx 60 feet, and not always, the car will start to slow and look as though it is "convulsiing"
as if i was hit throttle, stopping, and repeating very quickly?
doesnt seem to do that close at all?

which rc is it, electric or nitro?  Could be interference.  Does it happen at one place or everywhere?  Make sure you antenna i extended as high as possible on the car in the tube unless your using a 2.4 system, same goes for the antenna on the radio.

ITs an electric..actually an HSP but I  have put himoto parts in the car and figured they are fairly similiar.
It happens at the same distance, and its when I am turing the car around to drive it back
thanks

Sounds like interference, try it in a totally different place and see if it happens there too.