When the back door is open, lift up on it. Is there any play/wiggle? Are the hinge bolts tight?
When it's closed and latched, does it line up perfectly with the rest of the body?
Mine was acting up similar to yours, but no play in the hinges. I found that the latch pin had loosened and moved a bit. This can be loosened up and realigned, that may smooth things up for you. And yes, periodically spray some lube on all hinges & latches.
'01 60th anniversary ed. TJ 4.0 3 speed auto, 2.5" susp lift, 1" MML, 33X12.5X15 MTR's, weekend toy.