1999 Chevy Truck engine doesn't start

I have a 1999 4-door Chevy 1 ton truck, with a 7.4. I started the engine, let run for about 1 minute and when I put the truck in gear the engine started running rough. I put the trans in neutral, to try and clean the rough idle out, and the truck would not take any fuel and quit.
I checked fuel pressure and have 50 lbs during cranking. I replaced the coil, because I thought the spark looked a little weak. Still didn't fire. I replaced the dist cap and rotor. Still will not fire. I can spray carb cleaner into the intake, and the engine will fire a few cylinders and seem to want to start. But doesnt seem to have any fuel. The plugs are about 4 months old, appear a little wet and sooty. Has about 1/2 tank of gas, and fuel pump is about 4 months old as well (Autozone).
What should I try next?