Hi i have a 99 chevy silverado 5.3L
I have had this running issue where the truck will fall on its face if you step on the gas. I pulled a code and got one for o2 sensors so I replaced all of them.
If you unplug the MAFS it runs a lot better,(I tried to replace this to it didn't help)
I have tested every sensor and replaced the ones that were testing bad.
My fuel pressure at idle is 50 if its cold or warm when I step on the gas it goes up to 58 i think its suppose to be 60. when you take the vacumm line off the regulator it goes up to 58 and runs a little better... I had the fuel injectors tested and they said that they were testing good but failing mechanically so I replaced the ones on the even bank..I have done pretty much everything to this truck and still can't figure out the problem. I also had a fuel pump that the dealer gave me that had a bad sending unit on it so I put that in it thinking that it had good pressure but bad fuel volume that didn't help either I think I should replace the regulator but I want more input before I do that.
Let me know what you guys think
Thanks
Josh

Have you tried replaceing the Fuel Filter?
after everything you replaced I am surprised the regulator wasn't the first thing you replaced.

Does it run smooth, at slower speeds? I have a car that wouldn't accellerate, and after testing everything, it turned out to be a plugged catalytic converter. It ran fine, just wouldn't go. Sounds like you might have a similar problem, but I haven't seen others having this problem, so maybe not.

Good Luck!

well when I was doing the test nothing was leading me towards the fuel pressure regulator now I think that it might be that.
Yes I have replaced the fuel filter and I also have had the catalitic converters tested and they tested fine...let me know if you guys have any other questions.
thanks
Josh