+1 also replaced tensioner, no joy. Turns out it was the voltage regulator inside the alternator. Got a new one from RockAuto for ~$130 and was good to go.
I think my alt is a 105A unit... I was having some issues with light dimming but I'm also running two JL amplifiers. A .5 farad stiffening cap fixed that problem.
But back to original point: yes, you highly likely need to replace your alternator. It will get worse. Mine started out only flickering the battery light at high rpms. Then it became intermittent for minutes at a time. Then it stopped charging all together and I was stranded.
Spend the coin and remove the 6 bolts and 1 nut that are involved in the install. Very easy.