[decooney]

This happened to me once by mistake. Here is another easy check -

>> MAKE SURE THE PICKUP WIRES going in to THE MSD DISTRIBUTOR are NOT LYING NEXT TO or TOUCHING one of the SPARK PLUG WIRES.

I ran a plastic tube around the distributor pickup wires so it would not pick up any signal interference from one of the plug wires. If nothing else, check this for sure - this can occur exactly as you describe at 5k rpms.