2000 K2500 4x4 ext cab a/t 454 cid Been driving the truck without any problems. I leave work, it starts right up as usual. Stopped to get bait for 5 minutes, came out and it would not start. It just cranked over. Cranked it so much battery went low. Got it towed home, but haven't any clue what to check. I did replace the fuel pump 3 months ago and I can hear it cycle when I turn the key. Any ideas? I am supposed to go to a funeral tomorrow out of town. Please help!