Fuel Pressure help

[sheaadams86]

ive got an 03 yukon 5.3l flex fuel, when i drive it cruising seems fine, if i try to accelerate quickly it stumbles and hesistates and even stalls sometimes. i hooked up a pressure tester and its showing 0 psi key on eng off and an erractic 44psi when engine is running, tech data says its suppose to be 48-54psi key on eng off, why am i getting 0 psi? i know its hooked up right cause engine on is reading 44psi

 

[SnowDrifter]

I find the most useful piece of info, that also isn't dependent on gauge accuracy, is to watch the gauge as the issue occurs. Run it through the cowl and put it under the wiper or something. Does pressure drop when your engine stumbles?