[Yukon Jack]

The external voltage regulator is bolted to your radiator core support on the driver's side. Sounds like a good time to look into changing to an internally regulated alternator if the external regulator is causing your problem.

Are your present headlights a big power upgrade over the standard headlights? If so, maybe you should also look into rewiring them using relays to get more power to them.

Good luck finding the problem - I know how much I hate dealing with electrical gremlins!!!!