Carb rebuilt, engine still hesitates.

This is in my "C" body, but hey....It`s a MOPAR!!!

I have a Carter 6134-s 2BBL on a 1966 383. I just had the carb rebuilt by Carb-X. The car starts and idles perfect. Put it in gear...no problems. Once you get up to 25 - 30 mph the engine begins to hesitate. It does not die, and when you come to a stop it idles just fine. I have boilded out the tank, used compressed air to clean the fuel line, replaced sending unit, fuel pump, fuel filter and all vacuum lines. PCV valve is good. One part I have not replaced is what I will call the vacuum control valve ( I don`t know the proper name for it). It is located at the back of the engine and all the vacuum lines lead to it. Any suggestions?