I had an odd experience with the Glide during my return from the Sierras.
I was getting really bad fuel injection surging. At first I thought it was because I was riding next to my friend's BMW! Then it started popping and backfiring kinda like your Shovelhead.
At the next gas stop I removed the seat to see if my Revtech DFO had a loose connection. What I found was that the unit (which was velcroed to the frame backbone just below the fuel tank) had slid down due to heat or vibration or both, and was resting right near the battery. I pulled the unit off, cleaned the frame backbone and re-stuck it in its proper place.
The Glide ran perfectly the rest of the way home.
So was it heat from the battery or the magnetic field that was jacking me up? Or we could just blame it on riding in close proximity to a BMW Boxer!