I have no idea how long you owned your truck. If you are the original owner, then this may not apply to you. However, if you are not the first owner and don't know the truck's maintenance history, there could be something obvious that is wrong. I am thinking like an accident repair done improperly or with substandard parts.
My dad used to have a '57 Chevy that sat crooked. Could never figure out why. One day he counted the coils in the springs and found they were mismatched. Lots of frustration over what turned out to be an obvious, but unnoticed, problem. (I solved that problem when I got the car by re-doing the entire suspension.)
My point for the OP... Take some time and examine the basics. Do the springs actually match from side to side? Could there be an overload spring on one side that is not functional? Does it sit level when unloaded and do the springs look consistent side to side when unloaded?
A drop of "2-3 inches" side to side is significant. I could see a half to a full inch due to the load in the camper being heavier. That is a pretty good tilt, more than I would expect from just all the camper 'stuff' being on one side.
If you really want to break it down, you will need to load the truck with a heavy, but evenly distributed, weight load. I am thinking something like sheets of plywood. If it sits level, then the problem is with the camper weight distribution. If it sits several inches down on one side with an even load, then the problem is the truck and not the camper.
HTH!
-Eric
