I have a similar issue with my 2003 KJ, mine started after a Volvo rear-ended me and died from being punctured by the trailer hitch receiver (Also installed due to a recall item). This caused my tailgate to be be slightly misaligned. In the winter or if parked at an angle, I could not open the tailgate. As I cannot replace everything, I have found that lubricating the tailgate stabilizer insert (Section 23 Page 42 from the Manual Linked above for my 2003) has made it so I can open the tailgate year round. I have just been tossing more grease in March and September for the last couple years. After reviewing the manual linked by Billwill (Thank you!!), it looks like I can make an adjustment after confirming the exact misalignment to my my tailgate.
Yes, I could have sent a bill to the volvo driver once the issue was discovered. They already had a totalled vehicle as my Spare Tire pushed the front end in to my trailer receiver (Only had a cover, no ball installed) and punctured the radiator, and destroyed the Hood, Bumper and side panels. My KJ just had a small scratch on the Spare tire cover and the eventual noticing of the misalignment.