Jeeps aren't GM products, but I can still help. Have you ever had the transmission serviced? Chances are you haven't, and need to. Hopefully you haven't damaged your trans to bad by driving it for too long this way. Jeeps are known for bad rear ends, and transmission trouble. The trans filter is probably full of garbage/plugged up. If you did drive too long with it this way it will shift better after installing a new filter and fluid, but the damage is done. Also, just a heads up......if your rear end is making noise you better get that looked at too. I put all new bearings in the rear of my 98 Grand Cherokee limited to the tune of $360.00 my cost. I'm not sure what list price was, but it is quite a bit more. I've always liked the looks of the Grand Cherokee's, but beauty is only skin deep. It's the worst vehicle I've ever owned.