check the mast position sensor up front
when you turn the truck there is a steering sensor mounted on the pivot point that measures the position of the mast to tell the drive motors how to run according to mast position. If that sensor is not adjusted properly, not calibrated correctly or is bad when the truck goes into a turn the drive motors will not change direction or power properly and cause the truck to get in a bind and actually keep it from moving.
It allows the motors to react in the same manner like a 3 wheel sitdown truck works when you turn the steer wheel on it. Reducing the power to the inside motor and when in its fulcrum point actually reversing the inside motor in the turn. If this does not occur the truck just will not run correctly and do exactly what you are describing.