that kinda "between shifts slippage" happened to me with a ford and a Jeep. With the Ford it was also associated with extreme weakness in climbing hills (Cat) and the Jeep was here in FL. The jeep was almost fixed by adding Lucas "No-Slip" to the tranny as I would add tranny fluid. I babied it and got along OK until it was sold/

 

My 96 Blazer (4L60E), on the other hand; was slipping from OD to downshift on the Hi-Way for a while. (add Lucas) Then suddenly between gears on surface roads. Almost a week later there was no reverse and forward was more slip than grip. Lucas did not fix anything. 193k - 1st rebuild.