Ford Repair: 2000 Crown Vic P.I. 4.6 liter engine miss fire, blown head gasket, intake manifold gasket

Question
Diagnostic told me 1 through 5 cylinders were miss firing. I replaced intake manifold gasket. Computer seemed to reset, motor quit shaking while running til I got it down the road. Now the 4 and 8 cylinder are diagnosting as miss firing. I can unplug three of the eight ( one at a time of course ) coil packs and it does not put any strain on the motor. Unplugging the others obviously puts a strain on the motor. Do I have bad coil packs ? I replaced the spark plugs making sure of correct gaping. Could I have a blown head gasket ?  The error codes are P304 and P308 The engine really labors at high rpms ... but seems to settle a bit if you get up to speed an don't labor on the throttle.  Would greatly appreciate any input !

Answer
Hello Tim,
The first thing I can suggest is to start swapping coils around to different cylinders and try to generate a misfire on a cylinder that is'nt suspect. Bad coils are very common on late model Fords. Try to single out bad coils(the boots fail too, look for carbon tracking down the plug). By the way, use ONLY MOTORCRAFT COILS AND PLUGS! I see the most problems from knockoff products. Use that info and hit me back. Good luck.