I would pull the pan clean the screen make sure there are no broken springs in the pan add a magnet and change fluid.See what happens, a can of Lulcas Tran additive after you change would not hurt.If there no change i would start looking for a doner trans same year .I would not rebuild.
Mine had the exact problem when i first got it but mine would also rumble going in and out of over drive. 1st drain and fill fixed it for a little bit but was still had a rumble but not as bad. 2nd it was slight and my 3rd it was completely gone and shifting better than it probably ever has. Although i still had the 1/2 hard kick i found my tps needed reset and the idle screw wasnt to be touched and i learned it the hard way cause when you move that it also changes your tps voltage and it needs to be set with a feeler guage and than you set the tps to spec. I laugh at it because everyone told me not to touch the screw and i didnt understand why and even when it was explained to my i couldnt get it until i started messing with the tps voltage and using that screw to adjust the idle XD. But hey lesson learned its fixed and will not need to be fooled with again. But yes do a drain and fill and see what goes on. Than if it fixes it slightly than do another. And if all else fails check out the tps voltage. Should be between .4 and .6 when idle. Now when you set it if its out dont drive it hard till you know for sure its been set right. Because the problem i had was not knowing about the screw and setting the tps etc etc i had it set and idling good well it wasnt set the proper way and i peeled out of my drive way and drifted up my road its dirt and it slammed into second gear hard as hell and cause it to go into safe mode. Yeah and people wonder why i say my xterra is tough as nails lmao still running and shifting fine.
I doubt there would be. I am fairly certain that there would be no need for one. Though i had all these problems plus more. And if you go to a tranny shop dont let them talk you into a rebuild. Having owned my dodge with the 46re alot of tranny shops i went to said rebuild though i acted like i didnt know anything about it and just totally unaware of what needed to be done i could only find one shop that i could trust that gave me the problem that i already knew and it was the pressure solenoid but the problems where completely different than yours. In which the reason i say this is because there are alot of parts in transmissions and its always the suggestion of you need a rebuild and its complete bogus... Now 1 thing do a drain and fill not a flush. Pay attention to what comes out see if you can put a screen onto whatever your draining it into to catch any thing that comes out thats not supposed to. 2 if it fixes its slightly and your fluid isnt a nice red color do it again. 3 if none of that works start looking at throttle posistion sensor. And if all else fails than you need to have a machine hooked up to see if maybe you got another problem. Transmissions need rebuilt when broke slipping not shifting etc. Not when there is a problem of that aspect.
If you are going through all the trouble to drop the pan to clean the magnet and the filter screen, I would recommend just to go ahead and replace the filter seeing as it's cheap maintenance and you're in there already.