Here is what i would do.
Hook up a fuel pressure gauge. Pinch off the return line under the driver's door inside the frame rail. Turn the key on and if the pressure jumps over 80PSI, your pump is probably ok.
If the fuel pump can build that pressure then you have a bad/wrong FPR. The bleeding off of pressure is probably leaky injectors.
It seems like a real PITA to get to the FPR but really it's not that bad. I had my upper intake off so many times i could do the job im under 45 minutes.
If i remember right this one is said to work. I just can't remember if thats the one i used or an adjustable one.
Also from what i remember, The California emission equipped trucks will have the fuel tank pressure sensor. Federal emission trucks will not have that.