You probably have hiway gears (2.56, 2.73) in your rear end thus your low end will be slower than say 3.43 gears.
Also, the double pumper will bog down with this setup as your engine is unable to get hi rev's quick enough to use all the gas your double pumper is shouting into the intake.
First, find out what gearing you have. If you want to have a street racer then you wanna have something like 3.4+ gearing in a Safe-T-Track (POSI) Pontiac rear end.
I would also recommend using a stock QuadraJet /w stock 4 bbl intake.
