I have a lean on bank 1 & 2 on my 2004 corvette and have tried just about everything except for fuel pump replacement. I have changed out the MAF, checked fuel injectors, and checked for fuel pressure but I didn’t get any pressure while the car was turned to on and when I turned it to running it only had about 20psi. What can it be?

Your fuel pressure should be near 60 psi running...sounds like a possible bad fuel pump...if a bad fuel pump your fuel trims will increase from idle to WOT if you have a scan tool.

20psi is waaaay too low!
Are you also saying that it doesn't hold pressure on the fuel rail, after the engine is shut off? If so, this is also a problem.

It could certainly be a fuel pump issue. If you verified that the injectors aren't leaking down, then the check valve in the pump could be bad. Keep in mind that the fuel filter could also be clogged, or there may be some other restriction in the system that is causing the low pressure situation. I would be concerned that perhaps dirt in the tank is contributing to the problem, especially if the problem appeared soon after getting a fresh tank of fuel.

If it were me I would definitely suspect the fuel pump. IIRC the fuel filter is internal in the 2004 model, so be prepared to change the filter at the same time. And, while you are in there, be sure to carefully inspect for dirt and debris in the tank and flush as needed.