"Somethings that it can be:
stuck lifter- solution engine flush and oil treatment
Try CD2 in yellow bottle
Rocker arm valve lashing (high Mileage engine)- adjust valve lashing on all push rods, don't know how. Ask mechaninc
Alternator going bad-would see a drop in headlights while engine running, bad shaft bearing Alternator will get real hot, to touch.
try those, let me know what you find out."
Well, lifters can be fixed, but I wouldn't do it that way. If they're not pumping up then pouring some "magic oil" into the motor won't help. They can be reached "fairly easy" and I say that relatively.... The part about the valve lash is out of the question.. First, unless you're running solid lifters (which you're not) you don't have to worry about lash...the lifter takes care of that... Lastly, if was an altanator, it would more than likely squeal rather loudly.. But what you say is true about the light dimming, etc..