2000 Chevy Blazer misfire and sluggish at idle and from a s

had intake gasket fixed, and now the ses light is on, and there is a misfire code (ps301) for spark plug one, i have replaced plugs and wires, rotar button, and the distrubutor cap, still gives a code for a misfire in spark plug one, so i also have had injectors cleaned twice, checked vaccum hose, check every pressure line possiable, i also had a alternator installed with the intake gasket, the ses light comes on when you start it and then starts flashing as you accelerate( with a slight decrease in power), it will run rough until you hit 35mph or up, then it smooths out a little more, so i have been told it could be a weak battery, mass air flow sensor, head gasket, or even the intake gasket again, because i have statred to smell anti-freeze when the heater comes on, which i had to flush the heater coil when i got it back to get it working again, does anyone have a solid answer on what is wrong, and how to fix it