318 bogging at high rpm, but only in first gear?

I'm not a fan of cleaning up spark plugs. I'd put in new plugs, how old are the plug wires? What's the float bowl level, fuel line size from the fuel pump to the carburetor? Is there any rubber lines between the fuel pump and carburetor? I don't mean to sound disrespectful here but I have seen people install the fuel filter backwards. At what rpm's does this happen at? Factory springs are good for around 4500 rpm's. Even though I don't think it's your problem, but 120# of cranking pressure isn't much. I'm thinking that it's more of a fuel starvation issue than anything else. You may want to check out the condition of your fuel pump as well. Good luck