So I have a 2006 Silverado 1500.....don't get me started on this devil truck. It is a 2wd but has 4wd front suspension. Well HAD. Torsion bars and the whole bit. The problem I am having is I moved/replaced the gas tank. The tank is now under the bed where the spare tire used to be and now has a external inline fuel pump mounted inside the drivers fuel rail. I ran the line out of the pump straight forward to the engine and then the gas line coming out of whatever the hell the big black box is ( I can't remember the name right now) I ran back to the tank as like a return line.

Here is the problem. The truck runs great when started for the first few minutes and then starts to act like it is running out of gas. Once I get up to like 30-35mph it runs 'OK' ish (not really) but if I have to stop or slow down it dies and then won't start for like 10 mins(?) I wired the pump off of the old in tank pumps wires using a wiring diagram and like i said it starts fine. I read that I need 65psi for start and 40-43psi once it is running and the pump I have is putting out 100psi. I do remember seeing that the old tank had a tank pressure sensor which I don't have now but I am not sure how that would change the issue I am having now.

 

What codes are you seeing with a scan tool? That "black box" you talk about is probably the EVAP canister, and there are sensors and solenoids involved with venting the ORIGINAL gas tank on a 2006 Silverado 1500 and when the EVAP system is messed up or malfunctioning, it can cause performance issues. If the relocated tank doesn't have the sensors and connections into the EVAP system that the original had, it is likely that you run for a few minutes, at which point the EVAP system engages a solenoid to send gas vapor from the gas tank to the EVAP system, and instead, it is likely opening up the evap system to outside air. Much like the way modern vehicles run like crap if you lose the gas cap, and have the tank open. The pressure sensor you mention not having now is all part of that system, and the computer is checking all these parameters and trying to resolve data for something that no longer exists or is no longer hooked up right, causing things to run rough.

Your check engine light should be on, and I would make an educated guess that it is showing EVAP system related codes. Am I right?