Car runs really rough when cold

[Digger]

Heres something eles I just discovered, when the car is running rough I can let it warm up, then put it in 1st gear and drive at 3000 rpm for about 15 seconds, it still is running rough the whole car shakes then all of a sudden it smoothes right out instantly and throws you back in the seat. I have checked the fuel pressure when it runs rough and then smooth and it stays at a constant 7 psi. As for the engine I just rebuilt it. It has 302 heads, comp cam XE 258 cam, 4bbl cast intake, performer 750 carb and the rest is all stock. Im going to block off all my vacumm lines and see if that makes a difference. As for some of your suggestions I just had the head off and there were no signs of antifreez or oil burning. I dont think it is the valves or lifters because of the way it smoothes out all of a sudden. Maybe Ill try a different cap and wires.