...and FWIW I am still throwing P0171 and P0174 every time I go out. So there's something that still isn't right.

 

Tell Zippy you have those codes. Those are lean codes, and could be harmful to your engine.

Can you pressurize the system at all? Plug the exhaust so it will hold air, and pressurize the intake system. You should be able to hear a leak if there is one. Maybe you have a crack in your intake somewhere. Do the RPMs rev up high at first start up like there is a leak? It should go to about 1600 RPMs when you first start it.

 

It revs up to about 1200 when starting warm.

 

i remember having both codes pop up on my denali, had to change both O2 sensors i verified they were not working properly from a log i took. + it slowed the truck big time and had crappy gas mileage