gasser

Have you tried to 'fool' the fuel system by putting Cetane booster or diesel fuel down the intake? By doing that, you are bypassing any leaks ... see if the engine will run for a few seconds with diesel down the intake.

If you are ballsy, you can get the truck started by using Ether ... but you have to make sure your GP system is disconnected. You don't want your GPs on with ether in the cylinders.

I had similiar issues, where the truck wouldn't start without a shot of Cetane down the intake after sitting for 4+ hours. I thought I had a fuel air-leak or something. Turned out my GP system wasn't working at all. Totally tricked me another other folks - who shall remain anonymous . Even though you are getting volts to the GP themselves, they could be faulty. Have you changed them?
If you do the Ether thing, and it fires right up and stays running ... you may have a GP issue rather than a fuel issue.

Anyhoo, try the diesel and/or cetane booster down the intake to see if you can get it started/running on that. Hopefully that can give you an idea on what to do next.

-graham
86 M1009