2003 Chevy Silverado fuel pressure

I have had a engine code of bank 1 and bank 2 fuel trim system lean. I have replaced the fuel filter and the pressure regulator. I am getting a reading of 20 psi on the tester. When pushing the bypass valve on the tester it takes about 20 seconds to fill half a pint, I was told that it should fill 1 pint in 15 seconds. Is there something else I should check before I go tearing the gas tank out to replace the fuel pump? Engine does not start on the first turn of the key, it will spit and sputter and then fire up on the second. When I first turn the key on with the fuel pressure tester hooked up I get 5 psi, the 2nd turn I get 10 psi and if I keep turning on and off it will eventually get up to 20psi. Is there something I should check on the return line? Engine also lacks high speed power.