I have a history with MSD since I have built several Chevy motors using their complete ignition systems. The MSD 6A box has left me stranded more than once and that last time I was in heavy traffic coming up to a stop light. I pushed the clutch in and the engine stopped. I had to get my Jeep towed back home and then I replaced the box. I went through three of the 6A boxes before I sold the Jeep. Now forward to the Scrambler. I have a Chevy 6 cylinder HEI distributor that I converted to fit the 258 motor and I installed an MSD high energy coil brand new. I used a factory ignition module and Autolite plugs with the correct gap. I also have a quality cap and rotor with copper leads. I even put alot of time into setting the mechanical and vacuum advance curves to be perfect. From day one I have had a slight missfire in the motor and I could not trace it down. Also when I would come off a a higher RPM the motor would almost stall before settling back to its normal idle. I always figure this was my carb creating the issue. Last summer I switched over to to a used Howell TBI kit and the motor ran better but still had the idle drop issue. I just learned to live with it since I usually do not get alot of free time during the day to mess with tuning it perfect and it runs "well enough". So a few weeks ago the miss got real nasty and I was affecting my acceleration and drive-ability. I went through the whole ignition again and as usual the plugs were reading perfect and everything is in great shape. I have an extra Airtech coil hanging around and decided to change it out to get the MSD out of the equation. This morning I drove the Jeep to work and walla, it runs perfect. Great drive ability, smooth idle, no drops or stumbles. I thought I would have learned from my errors but this time I am done. Sometimes the aftermarket is not the way to go. The crazy part is I prepping a multiport 4.0 setup to replace the Howell next month and I am using the 4.0 ignition. If this heavy stumble didn't get worse I never would have bothered to even find the problem.