[BossHogg69]

This is going to sound crazy, but I had a similar problem in my '99 Tahoe last year. It would sometimes crank, but would immediately die. I too was thinking it was a bad relay or the fuel pump was going out. Sometimes I could mess with the ignition switch and it would go ahead and start, but then it got to where it would only crank and immediately die every time. I had a buddy come over and put his Cornwell scanner on it, it was saying the security system was not letting the fuel pump relay kick on - he was sure a new ignition switch would solve it. So, per his recommendation, I put a new ignition switch in and still had the same problem. I ended up having to take it to the dealer and it turned out the rearview mirror (w/compass & thermometer) was shorting out and was tied into the same circuit on the 'body control module' that the fuel pump 'run' relay was on. They just unplugged the rearview mirrow (I didn't want to spend $750 on a new one) and I've never had another problem with it.

I hate taking my rides to the dealer, but sometimes its a last resort. It ended up costing me $186, and I haven't had a problem since.