2004 GMC C2500

Engine Mechanical problem
2004 GMC C2500 V8 Two Wheel Drive Automatic 135000 miles

last night when engine started it ran very rough, missing badly. Turned it off and restarted after a minute, it stopped missing and ran pretty smoothly, when started this morning it was missing badly again and has a rather loud knock/ clacking sound from what appears to be the drivers side in the lower part of the engine. I changed plugs and wires but there is still a miss and knock.
February 2, 2010.

After it warms does it run smoothly? The knocking sound sounds like the flex plate is coming apart if you told me correctly " rather loud knock/ clacking sound"

Dr Loot
Feb 17, 2010.