engine issues, help please!

hey guys i just had my heads rebuilt on my car due to bad vavles. so i had a full rebuild. alright i put everything back together and the car ran pretty good for a day. then on my way home from work all throttle went away i could put it into neutral and itd rev fine. but in drive it would barely pull the car and would wanna die if i throttle more the 1/4. made it home and while looking over things i checked the oil. and its all white with antifreeze. a couple buddies said it sounds like a intake manifold leak. whats your guys opinion?