You're correct. Camper definitely isn't parallel with top of the truck bed. Again, is the bed the same depth front to back?
If yes then bed could be crowned a bit and camper not sitting down hard or camper frame a little bowed or squished in back.
Looks like the bed is also canted back looking at the bottom body lines.
Honestly frame looks a little tweaked from all the weight on the back.
Truck might be getting fatigued from the load?
How many miles, how many with the big camper and or trailer combo?
Does the bed line up better with the cab when the camper is off the truck?