Do you go down hill pretty fast? Is your governor and rpm limiter still in tack? If so, then what may be happening is rpms are reaching more than rpm limiter and it shuts your spark off. But when it gets back down below 3600rpms, it is supposed to tun your spark back on. It may have a problem and needs to cool down from a long desent down. Easy way to check is next time, before heading down, take a 10mm socket, a 3" extension and ratchet, and on the front of the engine down by the oil pan is a small black square box like thing mounted to the block. Remove the passenger side mounting bolt and there is a brown wire attached to that bolt. Remove the ground wire and tape it up and then try the desent down the hill and see if it still does it. If it don't, then your RPM limiter is bad. What you removed was the ground kill to your coil if the rpms reach more than 3900.