03 sierra pump problems and other stuff too-help please !

[motocrossracer8698]

Hi guys i have a 2003 gmc sierra 4.8 vortec 2wd. Its been acting up the past couple weeks first we noticed that it started stalling when the motor was cold mainly and every now and then when driving around town . it ran great except for the stalling when stopping and the idle dropping down real low. The check engine light was on the whole time but working my crazy shift at work i couldnt get by autoparts store to get it checked out . well after driving 30 miles or so friday it cut off on me and wouldnt crank back up i had to tow it home. I never could hear the fuel pump running i beat on the tank and the truck fired up ran about 20 secs then died again so i figured its the pump. I found a used one swapped it out now its doing the same thing it just ran little longer then shut off put a gauge on it it ran during ideling it only had about 28 psi and was jumping alot then it strated dropping it dropped to zero and then the truck cut off. I. So frustraited ive wasted so much money already i dont want to waste anymore. I bought a new pump i have it sitting here i dont want to install it until i get some feed back because if i put it in and it doesnt solve my problem then im out of 260 bucks and out of money too so if you guys could give some feedback on what to try before i install the new pump it would be greatly appreciated. Ive checked the harness around the tank area and it looks fine. Also i checked the fuel pressure regulator with it running it did t have any signs of gas on the vaccume side so i assume thats ok .

Also one of the times it was throwing 3 codes (while the battery was very low ) i assumed this was only because it was low it didnt throw anymore codes since now that its charged. The codes were p0120, 0220, and p1516 (ive heard that weak battery causes this ) the other codes are for tps sensor i replaced it and it didnt affect anything so reinstalled the factory one

[diyer2]

Stopped reading it. Drives me nuts when proper punctuation doesn't exist.

[davester]

Well, you could replace the FP regulator, which is relatively cheap and easy to do and see if that helps, but it is more likely that the fuel pump needs to be switched out.

[motocrossracer8698]

Is there method for testing the regulator besides looking for gas on the vaccume side?

[motocrossracer8698]

Just installed the regulator and no change its only reading 30 psi then it dropped to 0 after about 20 seconds of idling .

I cycled the pump 3 times before starting it up the 3rd time it sounded like the pump was dying out in the middle of pumping