I have a pa performance alternator and the same thing is happening.

Mine has all upgraded wiring and about 700 miles on the unit.

My light comes on from 2500-4500 rpm and lights dim, and everything goes back to normal under and above that posted range.

Jason 00 Audi S4, 2.7 Bi-turbo quattro 01 S10 Xtreme, 4.3l 98' Contour SE with some mods 96 Cavalier (beater)