How was the truck before it was torn apart? The orbitrol should have been replaced instead of rebuilt. I'd take a close look at the steer cylinder to see if it's bent, they were famous for that.
How does the lift ,tilt & sideshift operate? any issues there before?
Try to jack the steer tires off the ground and have the truck running and someone in the operators seat slowly turning the wheel in each direction,you watch the steer axle and try to see what it feels like when it moves, could just be air in the lines that need to be bled out.(I'm never that lucky though)