Transmission problem I think

[baseball_playa1575]

I have a 93' JGC and had the transmission rebuilt about 3000 miles ago. Ever since then going from 0 to 20 it feels like the engine is cutting out or something with the transmission. If I put it into 2nd and start driving it still does it. So I think it has something to do with 2nd gear. I have taken it back to the shop that rebuilt it since it has a warranty and everytime I take it back it wont do it. It will only do it until the vehicle is warmed up. I have checked the fluid and it is a lil bit above max. Could this be causing it? Any ideas? Thanx