Could you tell us how you lowered the truck? New springs? Lowering blocks? What sort of power steering setup? How about the drag link? Link parallel or sitting at an angle? Is the link running laterally or front to back (like the original)? Anything get changed with the rear axle/differential? Any visible damage to the frame, axle, anything make you think this truck got hit sometime in the past--maybe on one side? We're in the dark on what has been done. Bill and I and everyone else here really want to help you solve this problem asap. The more complete picture we can see, the more likely it is we can keep ourselves from running off into the weeds too much.
On the idea of front wheels and rear wheels and tracking: If you have something that is straight and long enough you can see if your back wheels and your front wheels are tracking straight (essentially they should be traveling in parallel lines with toe in at zero and the front wheels set straight, measuring at the center of the wheels). Even if the front and rear wheels are designed to be at different widths you can check this as long as you know what your universe is supposed to be. I've seen people do it with pieces of plywood cut straight and glued, channel iron, all sorts of things...I even knew one body man who would first measure between front center wheel to rear center wheel on each side and then wet a spot on the floor in front of each wheel and push the vehicle through those wet spots to get a clear picture of exactly where each wheel was going during its travel on any car which had been in an accident bad enough to have changed things.
