I'm in desperate need for some other suggestions. I have a 318 that won't start after it gets warmed up.It has a new timing chain,cap rotor,wires and plugs.The carb was working fine when I pulled it from another truck.It starts great and idles fine until it warms up-after that it hesitates and starts to backfire under load.

any help would be appreciated

When you say that it runs fine cold but hard starts hot it sounds like the air/fuel mixture is too rich,ie the choke is staying on.It doesn't make sense that it would also backfire under load,that sounds more like a mechanical problem like sticking valves in the guides.check for properly routed and connected vacuum lines.Emission controls not functioning correctly could also cause a backfire.You know what I bet it is,you said you replaced plug wires on this engine,I have come across this before,the firing order is 1-8-4-3-6-5-7-2.Number 5 and 7 are right next to each other in the firing order.That means that there is only 90 degrees of crankshaft rotation that separates the firing of these two cylinders.Since these are right next to each other on the same bank(driver side) it is easy to misroute the wires yet the engine still runs.Also you have to be aware of cylinders 8 and 4.If you mix these two up it will do the same.Also be aware of mutual induction from one spark plug wire to another,keep 5 and 7 as far away from each other as well as 8 and 4.Should be a quick repair.Hope this helps.

What is your timing set at? Is it advancing properly? Is the choke opening fully?
Just some thoughts off of the top of my head.

1) choke pull off valve
2) balustrade or ballast resistor
3) ignition module
Just guessing.

Thanks for the suggestions guys.I don't know specifically what it was,I changed the alt,batt,starter,voltage regulator,ignition module,and another set of plugs. it seems to run fine now so I don't care what it was.

Does it sputter and try to die when it gets hot? If so it could be that it is vapor-locking. Just an idea.