My 97 4.0 also does the same exact thing. I figure it's the sending unit, in the tank. You gotta figure the gas sloshing around when below half a tank, constantly works the sending unit, and eventually (170,000 miles on mine) wears that particular place out. I'm used to it by now, and considering the cost of a new pump/sending unit , not to mention having to drop the tank to do it, I'll just wait till the pump gives out first. I too, have a reman ECM/PCM, and it had no effect on the gauge problem. Just one of those MANY jeep things. But, I think we tend to forget just how old, and how many miles we have on our rigs. Most any vehicle with over 150,000 miles will also have a ton of problems. I do wish we had less computerized crap, but we got what we got. I would have never guessed that a 1997 vehicle would be so advanced with all the sensors, etc. etc. Like for instance, how many vehicles have a temp sensor under the battery? Or a low washer fluid sensor, low coolant tank sensor, etc. etc. When they all work, it's wonderful. When they don't, it can be a nightmare.