Originally Posted by M130ISWP
The exhaust place said it might be the fuel pump causing the flat spot.
That is actually a good idea. It could be the fuel pump. It could be mechanical issue with the pump, or even a voltage fluctuation issue at the pump. Or a ground issue at the pump.
Do you have access to an OBD-II code reader. Maybe you could read the fuel pressure while on the fly. Or install a mechanical fuel pressure gauge(temporarily) and drive WOT and see what it read at your flat spot. You will probably need a helper.