Is this for a GM or a ZF transmission? If it's a ZF, be warned that they have a revised design for their valve bodies as of last year. There is a problem with leakage past a particular plunger that causes slipped upshifts from 4-5 and/or 5-6.
I recently went 'round and 'round with a local trans shop that rebuilt my transmission (ZF 6HP-19) and they finally had to put in a brand new (2012) ZF valve body and eat the cost.
There are a lot of sub-par rebuilts and just plain junk used ones out there so caveat emptor.