I have a Nissan pickup in the family, '86 with 76,000 miles (FIL passed on & MIL won't sell it), that had sticky shifting. I used a 5 minute transmission flush, did an ATF flush (that first fluid came out black!), then added a bottle of Red. It now shifts OK, but whether the improvement was due to the flush stuff, or the new ATF, or the Red...I can't say.
I also have a Volvo that was shifting abruptly...this was about a year after an ATF flush. I added Red and it now shifts smoothly like it used to.
Ken