I've sen this in the army many times. The mechanics are parts changers not mechanics. They try to eyeball the rear end after replacing something and it's off causing the truck to dog track down the road.

 

On most trucks, big vehicles, its pretty hard to "steer"it from the rear unless its damaged. everything bolts together with no variables.
something must be bent! I once had a spring bracket with a broken pin that went into the axel mount. the axel shifted slowly till the tire touched! I bumped it back with a 4x4 beam and it was ok for years! that's the only thing that could make it dog track.
Hope we find out.

 

On the H1 and any other independent rear suspension vehicle, there are tie rods that keep the outer hubs tracking straight. They can be adjusted or knocked out of alignment just like the front tie rods. The difference is that the rears obviously don't make the wheels turn left and right. They just hold the hubs straight and true. If they are bent or out of alighnment due to damage or someone trying to eyeball it with a tape measure, it can cause this dog tracking situation.