Sorry, I meant equal power in both wheels from side to side. Reverse is about half the speed of forward. but whether you are goiing forward or backward, the power to both wheels is balanced.
You do have to make adjustements to keep going in a straight line due to ground undulation and control play. I'm not sure if what you are experiencing with you GS falls into this category or if you there is soomething more serious. If you are accustomed to pistol grip controls and not used to the "push to go" type controls, this might account for what you are experiencing.
Hope you get it worked out.