Thankyou for that had a feeling it was something to do with the pot!!! Or gears as you say thankyou for that least I know I looking in right place!!! Cheers gary

Hello
If it's 335-02 truck, it probably means, you have the problem with the traction pot or with the small gears linked with it.
All's located under the pedals, on the left side of the truck.
Check the plastic gears for wear, eventually replace. The same with the potentiometer.