newbi here just bought a 95 z71 with 5.7 needed head gaskets changed after changing them now it runs rough and has black smoke coming out of the tail pipe I checked for tdc and and set the timing It ran smooth before I changed the head gaskets it just had whit smoke but ran really smooth I'am stummped this is my first chevy. I know the black smoke is from to much fuel but when I took the left cyl head off coolant got in to the exuast could it be the o2 sensors or a vacume leak need help got any ideas.