Diagnostic help please

Think we need a little more info on the car and combination - cam, gears, trans, shift points, tire size etc.

Is the fuel system designed for methanol? Might want to verify timing at a higher rpm or at least see if its correct to fire the mixture at a higher rpm.

Also, a 750 vac. secondary might be on the small side for your combo. Have you messed with the jetting? Secondary spring rate? Power valve? Throttle linkage adjusted properly? Float levels in the bowls correct? Where are the filters in the delivery line? Why do you need two filters? What size is the return?

What's the rest of the electrical system? Battery in the trunk? Alternator good? Belts good? Dampener good?

Is it an automatic? If so, maybe your converter is inefficient/slipping badly at that rpm? Not likely though, I think you would see that on each shift. Just a thought.