1999 Ford F-150 • V8 2WD Automatic • 106,000 miles

Have a problem with my 1999 F-150 4.6 106,000 miles on it. The code says it is miss firing in cyclinder 5. The plugs and wires where changed and the coil block for that side was also changed today. It runs really rough and it you can feel and hear it back fire, could someone tell me what the problem might be. The engine light went off after it was changed. Now after driving it around the engine light came back on and it still reading miss firing in cyclinder 5 He did a compression test and found out that the cylinder is losing compression. It could be a possibility. Would this cause a miss fire and this did not happen until after the plugs and wires were changed I notice now that when I first start my truck up all the gages are doing funny things ie they all going back and forth for a few seconds this never happened before. Is this something elerctrical could be causing my problem?
January 6, 2011.

There were problems with the threads that the plugs screw into being too shallow. As a result, they would strip. Check to make sure the plug is tight and the threads are in good condition. You may be losing compression because of that. That is the only thing that makes sense to me since it happened since the plugs were replaced.