First start with the simplest adjustments.
Disconnect the rod that goes between the hydro pump lever and the lever of your hand control on both sides.
Check that the rollers by each handle are fully seated in the bottom of the plate with the notch. There is a bolt that connects both levers. If they are not both in the bottom of the notch than loosen that bolt and the rollers should move into the bottom. Tighten the connecting bolt.
Now adjust the rod that you previously removed so the bolt will fit into the hole of the lever with out moveing the lever. Tighten the bolt.
Drive the unit. If one side is faster than the other you can adjust this by loosening the four bolts, on the fast side, at the bottom of your hand levers, they hold the rubber boot also. Move the plate and boot back slightly and tighten one bolt. Drive it again. Repeat as necassary until the unit drives straight then tighten all bolts.
As for one side starting to pull before the other, you will need to be able to bypass the brake solenoid valve. If you feel confident that you can do that I will try to walk you through it.