1999 Chevy Tahoe intake gaskets

I have a 1999 chevy tahoe I noticed I was leaking antifreeze after some checking I noticed it was coming from the intake gasket on the pass side, after replacing both the gaskets and cleaning all intake and plentiun area and replacing the plentium gaskets. I put the entire thing back together. Replaced the distribitor cap and rotor plus spark plugs, then when I start it runs real rough and no power. Before I did the gaskets it ran very well and no check engine lights were on. Now I have a code 300(rapid missfire-random) cleared that and when I go to start it still runs rough as a 8 day clock. Any ideas would be so much helpful right now I am lost and having no idea what it could be.