I had been chasing this demon for several months on my 2003 blazer 4.3, it started gradually and got worst. I replace distributor with a new aluminum distributor, replaced cap, rotor and wires 3 times. The third set of parts were all ac delco. I kept getting arcing from the wires, mainly the the coil wire. After putting the ac delco wires on it started arcing out the bottom of the coil to the bracket. After thinking on it a day or so it occurred to me that if the coil was firing when the rotor button wasn't in the position to let the spark go to one of the wires that it was going to go to the easiest path to ground. Since it idle good and ran good until about 2500 rpms it got me to thinking the coil was getting a signal to fire when it didn't need to. The crank sensor gives the signal to the coil so I decided to make 2 shim washers from some electric motor insulating paper I had, each washer was about .0085 giving me about .017. I pulled the sensor and put them on, started her up and it was like a new truck, no more missing, arcing, tach steady and true. I hope this helps anyone else that's having this problem and sorry for being so long winded about it.

 

Glad to hear you got it right bud!

 

UPDATE!! Shims are still doing the trick, it's been about 4 months and still no problems.

 

Arrgghhh.. Havent we had this problem on here at least once since this?!!!!!
- of course that raises some other questions about wave shapes concerning the rest of the teeth on the reluctor used for missfire detection.. but, hey.. if it works, fix it later.

Good job!!!