Re: Tuning help
If the jets and metering rods haven't been changed from new, then you probably are having lean surge. The 780 Holley on our COPO Chevelle had #68 primary jets and there was noticeable lean surge at 60 mph. No power either. Getting the jetting and timing right made a BIG difference. GM was dealing with emissions by leaning out the carb and retarding the timing with a very slow advance curve it seems. Jim Hand is a Pontiac guy but he has a lot of Q'jet jetting information that would be a good ball park for your engine. Do a Google search for him.
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Chevelleless after 46 years......but we did find a low mileage, six speed, silver 2005 Corvette. It will just have to do for now. 
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