Dave ,
Just a slightly different suggestion than Jon G, more in line with the topic of this forum.
A lower level/lean on one side that includes your bumper may be a sign you have a rear spring and/or shackle problem.
Check the shackle to be sure it's still attached to both the frame mount and rear spring eye and has same stand-off as the opposite side of the truck. Check the spring for a loss of arch compared to the other side and for damage/breakage at the spring eyes on either end as well as possible cracked/broken spring plates. Also check the axle to spring mount at the spring and spring to frame mounts for cracks or signs of movement.
Oh yeah, might as well check the shocks and shock mounts for good measure.
Snap and post a few pictures of the truck rear suspension (both springs/sides) and that may lead to more info.
Dan
