Transmission Flare Problem

[Jmana]

I have been diligently searching the archives to find a solution to a flaring problem I have been having with my 87 300D, but haven't found anything that matches my symptoms. What's been going on is it has a flare between all gears that has been getting worse. It doesn't seem to do it when it's fully warmed up, or when it's under a load, such as going up a hill. But the flare is really odd, it's not just slipping, but it will also upshift, then immediately downshift, then immediately upshift again. Has anybody had this happen to them? I am pretty sure the tranny is good, it had a rebuild a few years ago and hasn't been driven much since then. The fluid level is fine, but I am going to drain it and put in Mobil 1. Any other suggestions?