2003 Chevy Suburban Low Power

2003 Suburban, while trying to accelerate engine will bogg down and miss. Starts fine, idles fairly well. Code indicated Mass Air Flow sensor. Added new one, no change. Checked fuel pressure at fuel rail. 42 psi with switch on, 42 while running, 50 for a second while accelerating then back to 42. Shut engine off and it slowly increases to 50 and with hold there for a long time. Checked fuel regulator by removing vacuum and pressure increased to about 52 as suggested by troubleshooting procedure. Changed canister fuel filter on frame and no changes. Cat Converters seem ok. By that I mean good pressure at tail pipe when holding hand over exhaust. No rattles at Cat Conv when tapped with hammer. Specs say fuel pressure should be between 55 to 60 psi. Any suggesttions appreciated, RT