Annoying Engine problem

[macblazer2]

So the specs:
1971 Chevy C20 Longbed with a 454 big block and TH400 tranny. Aftermarket distro (aka no points) Has a 750cfm Edlebrock carb on it.

I've been having an annoying problem that for the life of me I can't trace down. I'm leaning toward electrical so I'll probably replace the entire wiring harness at some point soon since the original is pretty hacked anyways.

When the weather is warm I see this issue more than I do in the winter when it is cold.

So every once in a while the truck will just suddenly act like it is only running on 4 cylinders (power just drops into the toilet and it starts sputtering and sometimes stalls out) and a lot of times if I just take my foot off the gas and let it coast it will go back to normal.

First I thought maybe it was because I was getting on the gas to hard and that was what caused it, but no...normal driving (not heavy acceleration and it will still do it)

The carb is brand new, the plugs are new, the PCV has been replaced, the distro cap and rotor look fine, etc etc.

"Seems" to do it mainly when it is under load. Meaning I can have it in the driveway and rev it and let it run and it has never done it under those instances.

Any ideas for what people think I should check or maybe haven't through of would be cool.

thanks!

Dale