For the qx4, remember the reverse lights are in the hatch, unlike the pathy, integrated in the tail light housing itself.
Otherwise, I went to the search bar at the top of the forum and typed in, "swap taillight" then "swap tail light" and I found this thread that says it's either easy or just needs a little modification:
1997-pathfinder-tail-light-swap-t514080.html
Side note:
For your other issue, I'd usually recommend you don't combine issues into one post as that makes it harder for someone browsing titles to find it and help.
I don't have an answer for it ATM, but I've seen quite a few threads on hesitation come up recently, maybe reading through one of those might give you some insight. Good thing yours is still driveable, right?