1967 Ford Mustang engine hesitates when you accelerate

1967 Ford Mustang Fastback mileage: unknown. The engine hesitates when you push on the gas, it idles fine, at about 1000 rpm, and it has a mild cam. When you take off, it has a hesitation, when you shift gears, (normal driving) it hesitates until you get your RPM up, it you are in forth gear and you push on the gas to go a little faster it hesitates. It has a new rebuilt Holley 600 dp and new spark plug wires, new distributor cap, Mallory ignition (Unilite); timing is set to 37 degrees TDC at 2000 rpm. 1-7 cylinders have 115-120 lbs compression, and 8 has 110 lbs.