My '54 Suburban was having the same problem: hesitation only when accelerating at high RPMs (under load, near the shift-point). After checking just about everything (including swapping out distributors, points, Pertronix unit, carburetor, coil, and adjusting timing from +/- 10 degrees from TDC), I found a very minor vacuum leak in the vacuum side of the dual-action pump (I had already isolated a minor vacuum leak in the wiper motor).
I disconnected and then plugged the intake manifold vacuum port and the truck now runs like a top (and it starts more quickly at all temperatures).
