2004 GMC Sierra Denali hard starting/idle problem

[Ralph241]

Hi,
I have a 2004 GMC Sierra Denali 6.0 liter AWD. I was driving and the engine stopped running. I got it to the side of the road and the engine will crank but will not start. It gave no indication of a problem at any time before this. I had the truck towed home and started messing with it. If I hold the gas peddle to the floor the engine will start. It will not idle or stay running under 1000-1500 RPM. When it does run it misfires extremely bad and smokes from the exhaust. It is getting way too much fuel. I don't have a fuel pressure gauge (yet) but I did take a screw driver and push on the Schrader valve on the fuel rail to see if I had gas present. It spits out a little and stops. I turned on the key switch and tried the valve again and same thing. I thought maybe it was a fuel pump issue but when I bleed the pressure off the fuel rail you can hear the pump run when I turn on the key. Once it builds pressure it shuts off. I am probably looking in the wrong area but have no idea where to start. I did pull a P0300 code from the computer but that looks to be a generic code.
Please help,
Ralph