Check your rear suspension mounts, specifically the upper arm mounts. They have a history of tearing off from the axle. If you are running nearly 400k miles, it is sure to have seen some stress. Mine has torn off twice in 200k miles (altho it was not fixed right the first time, my welder had some choice words about the "quality"! :bash:
It also may be the chain that holds your spare tire up underneath. Again, mine was thrashed; I had to cut it out.
The only other thing I can think would be the exhaust system.
I am sure that a little time on a creeper with a prybar or a big screwdriver, may help. A lift may be better, it lets your suspension drop to full extension and takes the weight off of it; easier to wiggle stuff.
Good luck, let us know!
Rob
