OK here is what I know about my problem. It only happens after the truck has been running for a while, and didn't happen at all in the colder weather. When it happens, the truck tries to stall, and the fuel pressure drops to almost 0. Sometimes the fuel pressure comes back up, other times it just stalls. Most of the time it happens when accelerating, but it has happened just idling as well. After it stalls, or tries to stall once, it will keep on doing it unless I let it cool down. I replaced the fuel pump resistor with no luck, I jumpered the hi/lo relay and it fixed the problem, but then I replaced the relay with a new one and the problem came back. What could be the problem if jumpering the hi/lo relay fixes it (or hides it) but the actual relay isn't the problem? What could the jumper be hiding?