408 breaking up

I've heard of that before never gave it a thought thats anothe reasy one to try. I 'm leaning more towards a electrical issue for now as i've got a miss even cruising @ 30 40 mph @2000 rpms. The more I think about it problem was not there before I installed the box.Last year on my relatively stock 340 this same carb went over 6000 rpms no sweat, so I'm gonna take the box out of the equation and see what happens. Still interested in other ideas though. Thanks PETE