I fought that problem forever on my 87, liked to drove me nuts. I tried everything in the book first, as I was new to Renix jeep repairs, worked on the engine, the exhaust, the transmission, many of the controls, then it turned out to be a bad TPS on the transmission TCU side of the TPS (the side that the old renix manuals never mention testing until about the 1990 FSM). It also had a bad, poor ground on the TCU side of the TPS, which together had it upshifting at 1100 rpm at WOT, so I was in 4th gear at about 25 mph! Took about 3 minutes at WOT just to reach 55 mph! New TPS and new ground wire for the TPS (new ground on both sides!!!!!!!!!!!!!!!!!!!!!!) fixed all sorts of issues.
Search for my old thread "The RenX Files" for the story and the data on testing the TPS first with a multi-meter, ohms and volts.