2001 Chevy suburban 5.3L fuel pressure help

[wellshii]

Those o2 sensors,have you tested them themselves? 300,000 miles is quite a bit.
Also,tried cleaning your MAF?
Checked for exhaust leaks as well?

[d4g4m]

Looks like you are blindly thinking about what to replace next. Get a repair manual for your vehicle. Chilton might have one. I had a 'no start' 'fuel injector delivery' problem [as per the CPU code] on my old Honda and was spending money on parts I didn't need. Bought a Chilton manual for my year/model. It's as thick as a Manhattan phone book. Very helpful. Also helpful if you have a multi-meter.
Manual lists problems and step by step sequence of trouble shooting. Problem was resolved by replacing the CPU [rebuilt unit]