Mine was doing the same thing with only 3000 miles on the engine. My buddy came over and said because of the MSD throwing so much spark it was probably the distributor cap and rotor. I wouldn't of believed it until he pulled the cap. DAMN!! There was quite a bit of built up on the contacts. He hit it with a little sand paper and it ran like a top. I replaced the cap and rotor and cant believe the difference. Hmmmm......... He told me that he replaces his every season along with the
oil.