You can get an ajustable vaccum can. The one you you have must be 25 deg. adv. If you also at 20 deg of mech. That is a total of 57. What is your total at 3000 rmp? What is it at 3000 rpm with the vaccum unhooked?
Port vaccum increases as you accellerate, but can also cause the car to run hot at idle. Not enough vaccum advance.