429 wont run! Help fast please.

[Coupe Devil]

I have been having all kinds of trouble out of my dads truck. It is a 82 model 3/4 ton two wheel drive w/ a 429 and c-6. It wont run at all hardly. Here is a list of what I've replaced. Cap and rotor, plug wires, pickup coil in distributor, rebuilt the carb, ran totally new fuel line, fuel pump, new filter, new coil, new battery, replaced "brain box", cleaned out fuel tanks. I think thats everything. The only thing else I can think of is timing. If you crank it it will somewhat run for a minute at an idle. Once you start out on the road it will goes for about a half mile (If I'm lucky) and it cuts out. It doesnt quit immeaditally it starts acting like it is starving for fuel, or isnt getting spark. I have checked both and the carb is working right, and I am getting fire to all plugs. Any help would be GREATLY appreciated. The truck is doen know and I need it.

Thanks
Brad