On mine I had a similar situation. I have a number of things that pull power (electric engine fans, stereo, Halogen lights, etc) and went through 2 100 amp and 2 140 amp alternators before biting the bullet and purchasing a PowerMaster 200 amp alternator from Jegs.
Had to modify the support bracket (cut it and welded in a 3/4 inch piece of steel to accommodate the extra size) but no more battery and power issues. Ammeter stays pegged at 14 most of the time and only when I have everything running (AC, fans, stereo and lights) do I see it drop to 13, even at idle.
Fixed my issue anyway for what it's worth.
