93 Ranger Transmission Problem

I have a 1993 Ford Ranger XLT 2 wheal drive, 4 cylinder with automatic transmission.The problem is when the transmission gets up to operating temperatures it will not change into gears smoothly. It starts out slipping (RPMs jump up) between second and third to the point I must lift from the throttle to make it engage. The longer I drive it the worse it gets between all gears when I have to stop or slow way down and go through the gears. I am fortunate enough to only work 10 miles away from home with only a couple of stop lights in between. The transmission fluid looks good and the level is fine. Does this sound like a major problem that is going to require a re-build or an exterior problem ?