Does it cut out in 1st and 2nd or only in high gear?
Adam has the best suggestions as to your problems. Check the sending unit sock and fuel filter.
Carb size won't be an issue at this point. Yeah it's small, but I know cars that run 11's with 500 cfm carbs.
Bigger metering rods = leaner BTW. If you want richer you need to install thinner diameter rods.
If you feather off the throttle slightly and roll slowly back in will the car pick back up accelerating? If it picks back up = fuel starvation. Does it blow black smoke like a deisel? An excessively rich condition can cause the same type of situation, but, I don't think that's the likely cause. I think it's lack of fuel.