[niles]

I had exactly the same symptom, using a holley 750 vac; using the proform center body.
Roll on works fine, 2200 slam to floor; heavy boog then takes off. Springs from heaviest/lightess no difference.
I had a cleve expert ride in it ; he said sounds lean as the secondaries open; recommended changing the squitter cam to smaller intially and more later. Nozzles are #32. Changed cams from the orange to one that had less early and more "later" lift.
Trace the cams on some paper to see the different profiles; they is only about .010 in differnces in many of them.
Bottom line, and much to my surprise, the new cam; I think it was the green or purple fixed the problem. Make sure there is no clearance under the cam follower; as soon as the throttle moves the squirt should start; even moving the curb idle screw changes this relationship.
I havent felt it stubble once since the cam change; so I'm leaving it alone. Although I was thinking of leaning out the mains because my plugs are dark.
gn