I recently installed a used gas tank and sending unit, and with this new one, sometimes when the car hasn't fully warmed up yet, the engine will barely be able to get enough fuel to run...but this goes away as soon as the car is fully warmed up, and once it is, my engine gets PLENTY of gas I can WOT on the fwy and it's fine...it's not turbo ( yet ) if that matters, but it's just super weird to me that it has a really bad problem getting gas. I recently also used that fuel injector cleaner on the first tank of gas I put in the new tank. The only thing I can think of, is that the connection between the fuel pump and the hardline that goes out of the tank has a slight leak which causes the holding fuel pressure to go down while the car sits for a few hours...but it's still weird that it doesn't get gas until the car is FULLY warmed up. Any ideas/knowledge? Thanks

 

Hook up a fuel pressure gauge and see for yourself. Not like anyone here can sense the problem, you gotta post some results if it's what you're thinking.

Also, it may be a voltage issue to the pump. Hook up a voltmeter across the wires going to the fuel pump and see what kind of voltage it's dropping.