ok just got done putting in new gm transmission 4l60e and it drove fine for like 5 mins and then no drive or overdrive first and second are fine but drive and over drive feel like neutralnot slipping at all just like not in gear what can it be??

 

i had the same problem, but mine was a stock 4l60e tranny. one day it felt like it just decided it liked not being in gear. i ended up having the tranny rebuilt, but a few months later it started slipping and not going into overdrive. the shop ended up having to give me a new tranny, they said there had to be a crack in the casing. since you just put yours in, i would take it back to where ever it was done (unless you did it yourself) and contact where ever you got it from..hopefully theres a warranty.