1997 GMC C2500 This is killing me.

I am now having a starting problem. It would crank and crank and crank, but not start. I tried cycling the key four or five times, and it started. It didn't always take that, often it would start right up, and intermittently it would take running the fuel pump a while first. Finally, after running an errand, it quite completely. The fuel pump wouldn't run, but it would turn over, and crank, and crank, and crank.

So I then replaced the fuel pump, and it started and ran just fine. Tonight, I went to start it, and nothing. I tried turning the key to let the fuel pump run, nothing. I tried a lot of times, nothing, dead, but it would turn over, just not start. Then, I let it sit for about an hour and tried again, and the fuel pump ran. I cycled the pump a time or two, and then it would cycle again. Same problem, and the truck would just turn over and not start. One of my brothers jokingly said to try turning the four way flashers on, and the fuel pump cycled and the truck started? I couldn't believe it, so I shut it off, and tried again and nothing. Hazards again and the fuel pump ran and it started. After letting it run for a while, it starts right up now.

Does anybody have ANY ideas? This has me STUMPED. I can't figure it out. I did test the relay before sinking $260 into a new pump. The relay had continuity between the right studs.

Thanks a lot.

God bless,

John