Check the normally closed side of the forward contactor.
Also If you get the steer angle just right you can isolate one drive motor form the other. By steering to almost 90 degrees the one drive motor will cut out, opposite 90 degrees will cut out the other drive motor.

Hi Jplayer, that was what I was doing when I found the ground in the motor. I'm really crossing my fingers that this is the cause of the problem. Probably know by Tues or Wed.
Thanks.

ok sleepywheel,
you found a short to ground in one motor
could be
do one other thing when you get the motor back in the truck
check the battery for grounds to frame on pos and neg sides
if you have any take the battery out and isolate it away from the truck frame so when you have it plugged in that will not be interference with your testing. reason i say this is battery shorts to frame can cause all kinds of strange problems, if you take that source out of the equation then finding other ground shorts are easier :o)
good luck

Well, I spent a few hours on it today. I could only get the F code to show up in reverse but not at all times. All I have to do is touch the accelerator in reverse, hear the left contact pull in, and then release the pedal. About 50% of the time F code would pop up and shut down the machine. As Jplayer and mrfixit suggested, I checked the fingers in the logic connector and had a quick look at the accelerator. I swapped the direction contactors around, thinking that maybe the double acting contacts were not making/breaking at the right time, then on to trying a different logic unit, swapping the diodes and transistors around without any luck.

I did find the left drive motor had an small short to ground at the field coil terminal so I pulled it and sent it out to the motor shop for inspection. Hope that cures the problem but I'm not convinced.

sleepywheel,
the "F" indicator is the Failure Protection Circuit warning code
if any condition is triggered that could cause the operator to loose control of the truck speed, or a condition in one of the drive circuits the logic deactivates the line contactor which shuts the truck down.

you can try what mrfixit says and check the connections at the logics but also direct your attention to the accelerator, it has led pickups inside it and if any of those gets dirty and causes any of the segments of the acceleration circuit to not function it can also trigger this symptom.

I had that problem once with one and it was a poor connection on the wire harness plug which has those tiny pins, in the back by the controler