Motor is a 350-300hp crate motor, stock except for headers and a Holley 700 cfm carb. No problem at idle or acceleration. Was wondering if maybe it could be a little rich on the primaries with the stock 700 carb.?
you need to check the timing at crusing speeds to see if its got too much timing or possibly you could have an igniton miss like a wire arching to the header tube. Are you running vacuum advance? disconnect it see if the miss goes away. Carbs that come out of the box are usually 2-3 jets sizes rich but not enough to cause problems. Be sure the float level is correct.