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96 Chevy K3500 with the 5.7l It has about 215K miles. I am trying to diagnose a fuel pressure issue. My truck first started to run rough like it had a miss. Check engine light came on. I had codes for both banks being lean. I cleaned the MAF sensor with no change. I checked for vacuum leaks. I hooked up a scan tool and checked the LTFT for both banks. They are both at 25%. I hooked up a fuel pressure gauge to the rail test port. Key on engine off it is around 45. As soon as the pump shuts off it almost instantly drops to 0. I am trying to figure out if I have a bad check valve in my fuel pump or if my FPR is bad. Before this all started, I noticed a loss in power. It could barely get a trailer up the slightest incline. I was trying to see if I could find out the difference in the speed of fuel pressure dropping when the check valve in the pump is bad and when the FPR is bad, to try and isolate the issue.