Car runs really rough when cold

[Digger]

I just rebuilt a 351 and put it in my 76 Ghia. It has a comp cam extream energy cam, 4bbl manifold and a new edlbrk performer 750 carb/w electric choke. The car runs really rough when you start it, it sounds like its missing, I drive it for half a mile, still rough and gutless, turn it off wait 5 seconds start it up and it runs like a top and has alot of power. I thought maybe the carb, so I switched it with my 750 performer that was on my camaro, same problem. and the carb from the mustang worked great on my camaro, so its not the carb. The only vacuum lines are the vac advance, pcv valve , brakes, and a vacuum line going to the trans. Any Ideas on why its doing this ?