You shouldn't run that carb with over 6.5 PSI. At 5.5 PSI you shouldn't be getting fuel starvation, at least not from the fuel pressure side of the equation.
With those 2.94 gears, and depending on your cam specs, it may be just waiting for the rpm to climb into the operating range of the cam / intake manifold before it can breath and pull properly again. Have you tried holding it in one gear to see if it will eventually get up and go, say around the 3000 - 3500 RPM area?