I know this is an old post but these fans draw as much as 29amps additional load on the electrical system. Most factory Alts on these tahoes are good for 105amp total. And there is typically a 10% buffer for any additional electrical draw(10amp cushion). The 105amp Alt puts out 85amps at "IDLE." So, just buying a 180amp Alt isn't going to necessarily fix the draw issue if it's Idle amperage is 85amps or less. That additional 29amp load will draw when your vehicle is at idle. So you need an Alt that will handle your max electrical load at idle as well. Your factory Alt is meant to handle all stock accessories when on at once at max power. So, factory Alt 105amp and say you add these fans which draw 29amps(they will draw full amperage pretty consistantly) so you need an Alt that not only has a max Output of 134amps or more but it needs to have an idle amperage of 134amps as well. Most aftermarket Alt companies dont disclose their idle amperage numbers. If your Alt is 180amps but has an idle amperage of 85amps then these fans will draw against your electrical system and cause issues.
I have a DC Power Alt, 190Amps max but puts out 135amps at hot idle. 140amps at Cold Idle.
I basically added up all amperage draws from additional accessories installed and future additions (stereos, lights, etc..) Came to about 80amps additional, added this on top of factory Amperage so a total of 185...went will the 190amp Alt to be safe.
I mention this b/c I bought a beefed up Alt from Power Master when I 1st installed these fans and I still had a crazy draw at idle. This caused the wires from the fans to get hot and melt and drained my battery. Went to DC Power website and learned about the importance of idle amperage.
Didnt mean to ramble