NEED HELP with Fast efi set up

[*71SWB*]

I've posted many times before I am a NON-MECHANIC and hope that I can explain my need correctly.

I have a 71 SWB C10 and purchased the Fast EFI master kit. Once the shop did the install the truck would run great for a short time and then lose preasure which caused the truck to cut off or bog down then cut off. They called FAST and were told the fuel pump was bad. I purchased a new one from them and plan on returning the defective one.

They then installed the new fuel pump and the truck did the same thing again. They again called fast and during conversation the mechanic was told the tank needed to be pulled and to have an in line placed on the top and an exit line on the bottom of the tank directly under the in line so the were in line with each other. The man from fast explained the pump does not suck the gas. I paid to have the tank removed and these lines placed in.

The truck was placed back to gether and ran great for about 50 miles. Then when I picked it up and had gone about 10 miles it did the same thing again. The mechanic checked all the readings and they are indicating as they should. With the engine running the preasure is at 43 and when you tap the gas pedal the preasure drops to below 20. My mechanic is telling me the fuel pump is bad again that the preasure should not change with pressing the gas pedal.

My mechanic will be calling fast today again. I'm hoping someone can shed some light for me. Is the pump bad or what else should we look for. I can't keep spending money. This system and install has cost me a ton....

Thank you for any help and I hope I've been able to explain this well enough for a mechanic to understand.