2000 Chevy Truck starting troubles

2000 Chevy Truck V8 Two Wheel Drive Automatic 110k miles

hey guys,
I changed my fuel pump, relay, and battery, alternator about 6 months ago. Recently, my truck will not start, especially first thing in the morning, it turns over fine, the voltage is good, I hear the fuel pump priming, I have new wires and plugs, getting good spark, have a clean k&n, cleaned throttle body, etc. I had an issue like this except accompanied by the security light flashing a while back, but I changed the ignition and this problem is solved. The truck fires right up with a small shot of starter fluid, and runs great after that, but it still gives trouble starting even after sitting only a few minutes (takes at least 2 tries). When I try in the morning, it will run for under a second and shut off like its out of gas, or a security holdout. But I know the pump, relay, and security system are ok, any other ideas? I really appreciate it. By the way, its a chevy c series 2500hd with the 5.7 liter 350.