Jerky at Slow Forward Speed Only

[fergie_38059]

Hello all !!
My 88’ DS jerks 2-5 times when I’m trying to just creep around the yard or while deer hunting. It jerks real bad to where I have to either go fast or just let off the throttle. Sometimes I can find a sweet spot where it won’t do it. It has an Alltrax controller with speed dial and Alltrax throttle/peddle. Aftermarket high torque motor. Heavy duty F/R switch. Heavy cables. Trojan Batteries. Lester on board charger.

Note: It does stay outside. Does not do it in reverse.