I have a 1990 Dodge Ram-not modified.
Injection pump replaced about 6 mo/6k miles ago. Truck is pretty much stock other than that. 111k miles, meaning this truck wasn't driven much.
I recently noticed the truck would take longer to start. Then a few days later it was almost like it wasn't going to start., even right after it was shut off. I noticed the fuel filter was like half full. I replaced the fuel lift pump. Problem went away. Next morning, truck was a little difficult to start again, but not as bad as the previous day. Then, at idle, truck died on me. Towed it to the dealer, they replaced fuel lines, filter, and pre-heater. Didn't make a difference. Truck won't start right after turning off, starts right up after I bleed the injector lines. Runs fine at high RPMs on the freeway. The longer I run it it will die at idle.

I pulled the gas tank, and started replacing rubber lines and pulled the strain/return line assembly out and replaced the rubber line in there. Nothing looked bad actually. I doubt that's the problem. Unfortunately I broke the hose fitting plastic piece as I was installing, so now looking for another one of those. So I can't see if that was the problem. I'm thinking it wasn't though. Suggestions?

There are no fuel leaks anywhere. I was thinking a bad rubber fuel line was letting air suck in, but the lines didn't look bad. I've never had this happen to me before.... but do you think it's possible my new lift pump went out on me right away? It's like it was running better for a while, only that day though.

 

Sounds like you've got a pretty good idea where to look. Don't forget the primer button. I replaced nearly an entire fuel system before I found a crack in mine. It was a brand new lift pump, too.

 

Same thing happend to my 97. It was just a small crack in the fuel line...actually a small pin hole. I had no idea it was even leaking but it was. It leaked just enough to get some air in the lines.

 

I replaced all the rubber lines on top of and inside my fuel tank. It runs better now... will at least restart after a handful of hours, but not 100%. I noticed some wetness on a banjo bolt for a fuel line that connects to the lift pump. I took this off when replacing the fuel pump. I tried retightening and moving around the copper washers. Made it worse. Now I'm waiting for the copper washers to get to me in the mail. Hope that solves it.

Everything on the fuel system except the injectors (don't know if they can cause this) is new on this truck now. So if it's leaking it's a metal fuel line or some copper washer.