no fuel rail pressure 06 2500hd
 

hey yall i work at a local mechanic shop and we received a 2006 2500hd completely stock truck from a car dealership. they told us before they bought the truck 4 injectors were replaced at another shop and is still running rough. i hooked up my scanner and saw #5 injector and a balance value of 7+ so i replaced it. truck started great and ran for about 10 min. before i went on a test drive. about 10 min into the test drive the truck dies like the key was turned off. got it towed back and found out theres was absoulty no fuel rail pressure. we thought it was the cp3 so we replaced that still no pressure. i tried unplugged the regulator with no difference. ive tried to pump the primer, taking the return line off going to the tank ( when cranking it pumps fuel out ), checked and shimmed the fprv, put a new pressure sensor on it, took the return lines off the injectors to make sure one wasnt bypassing all the fuel, took the fuel line from the rail to injector off (no fuel coming out while cranking). i'm coming to believe that the new cp3 from the dealer is also bad but its hard to believe. any help would be appreciated.