I have a bone stock 5.3 from a 2001 Silverado in my 47 Ford Hot rod. It has a cable operated Tbody, Turbo 350 trans and has been reprogrammed for this use. It occasionally hesitates under low speed acceleration. It clears up in a few seconds. Seems to happen after hard acceleration or after revving the engine. Shows no codes.The fuel regulator and manifold vacuum sensor have been replaced. Fuel filter is ok. Any help would be appreciated.

 

Hook up a fuel pressure gauge and monitor the pressure since you apparently have figured out how to replicate the issue. Maybe the fuel pressure somehow drops after the acceleration or rev-up?