This past summer I did an engine swap with my 87Iroc with a new 355 and after installing it I decieded to get the tranny flushed. The car never slipped out of gear before the swap but after I couldn't stand to drive it. It would drive well sometimes and other times not so good. I brought it to a local tranny shop and they couldn't see any chips or anything. Looking for some insight before I rip it out. Could it be the torque converter? I was reading in Super Chevy that not getting a burnt PCM could cause the tranny to slip. That is the only thing I didn't do. I read that as long as you bumped up the Fuel pressure it would compinsate for not having to buy a chip. Any leads would be great.

TIA
D