I just had a rebuilt 700r4 put into my GTA, it was originally in a '92 GMC van but the transmission guy had it already rebuilt and ready to go (the van owner had a heart attack and died before he could get it back). It shifts good for the most part, but under normal light driving I sometimes notice a very quick slip before it shifts into 4th gear, the slip is maybe 1/4 second. If I "get down on it" I don't notice it at all.

Is this normal? Maybe because it isnt broke in? It doesn't really cause drivability issues, just noticeable to me if im watching the tach. The guy that rebuilt it is very reputable, so I don't doubt his work. It does have a 12 month 12k mile warranty. I'm just not sure what could be done to it if I were to take it back to him.

 

The selective length servo pin may be just a click too short. Put a dial indicator on the servo cover and push it in with a hammer handle. About 1/8 inch movement is typical. I set them up with a target travel of .090.
If the travel exceeds 1/8 inch, you may have an easy fix.