so check everything you did, the condition of the wires (on might have been damaged in removal) and mist the coil pack to check for arching. Also did you lose any oil into the spark plug well when you did the valve cover gasket?
that would potentially cause the plug to ground out nit fire as well..
Slow day at work today, so I decided now was a better day then ever to replace my spark plugs. I ran out to the parts store quick and picked up some NGK Iridium IX's, pulled my car into the back of our warehouse, put them in. Initial start up was nice. I hope they work good. But to my point... I have a biased opinion to recommend NGK Iridium IX's since I just purchased them! He he. They were $20 for a set of two (they came in singles or doubles). So you'd be looking at $40 bucks for all four. Hope this helps!