[tranz am]

I would suspect an electrical connection is at fault for this. make sure all the connections are solid throughout the entire system. Not just in the fuel system also check the truck wiring specifically at the fuse box connections and ignition switch. I had a phantom problem like this before and after months of frustrating stumbling issues hunting my truck and pissing me off, I finally figured out it was the damn ignition switch with the loose connection causing me all the grief! Who would have thought right? Sometimes its the smallest of things you don't think about. Check the ignition switch , It might just be the culprit.
also don't forget to check your ground straps from the frame and body. Make sure the shop soldered all your wire connections too.