Todd,
if your having drive problems and the wheels do not seem to be pulling correctly you'll need to use a 5000 psi pressure guage and check the pressures on the drive manifold. It should have a diagnostic nipple port on the side of the function manifold to check pressures.
System relief (pump1) = 3500psi
System relief (pump2) = 3500psi
Lift relief (model GS-2668RT) = 3500psi
Lift relief (model GS-3268RT) = 2000psi
Steer relief = 1500psi

Now one thing i would do is check the valves for bad orings or damaged or stuck plungers.
Alot of the time orings will go bad and cause a pressure bleed over into other hyd circuits and create pressure issues with these other circuits causing them to malfunction.

There are 2 valves that control the oil flow to these motor circuits and it sounds like one of them is bad.
On the function manifold schematic it shows Valve A as follows:
DO3 valve, 3 position 4 way - A - Controls flow to the steer end
ground controls side drive motor
and the non-steer end engine side
drive motor in forward and reverse
And
DO3 valve, 3 position 4 way - B - Controls flow to the steer end
engine side drive motor and
the non-steer end ground
controls side drive motor in
forward and reverse

These 2 valves are the large valves mounted on 2 blocks on the function control valve, they have solenoids on both ends.
The manifold block should have stamped in it the valve letter designation A or B.
If you need the service book on it you can go to genie's website and download it, it is free to get for the public. it has everything you need to help identify where on the manifold these components are.