I noticed last night (first time i have driven at night in 6 mos)At low idle ok but anything above that and everything fluctuates. This morning cleanes batt post and connectors, checked evrything over and still does it. I can see it in the seat belt indicator, I can see the tensioner move with the fluctating keeping pace and when it goes back down to low idle it stops. I replaced the tensioner months ago because of noise. Any ideas?

take a multimeter, and check the voltage at low and high rpms, it may be the internal alt regulator going bad....

other than that, check ground wires and things like that as well........

-Lance

I had the same problem and ended up having to change the alternator to fix the problem which was the voltage regulator going bad.