I have a 2001 Sportage with approximately 124,000 miles. When I reach 3000 rpm and higher I loose elecrtric power where my lights will start to dim (both headlights and dash lights) even to the point where the radio will shut off and the air bag warning will go off. I have had the battery checked, and was told it was a little low, but not enough to cause any problems. They alternator checked out bad while on the car, but was OK when I took it off. I still think this may be an alternator problem. Any suggestions?