When I did the pulley/fan swap I bought a brand new 130Amp alternator off of a denali on ebay. Works great. Has a little voltage drop when the fans come on high. It drops a little bit (can't remember exactly how much) and the lights dim slightly. Works good though.

 

I just picked up a 200amp alternator off of ebay from DBelectric. That definitely took care of the voltage drops from the alternator/stereo/lights on my truck.