So in my 04 2500 Sub, I originally added an auxilary fan in front of the a/c condenser per a GM tsb on inefficient a/c cooling at idle. This tsb has the fan wired to the a/c clutch circuit so the fan is on anytime the a/c is on. Later I retroed a set of 06 tahoe fans in. They bolt directly in. I got a whole fan harness with the factory relay block and fuses from a bone yard , installed like the factory did it in the 1/2 tons. Just needs to be programmed. In the the mean time i made a 2nd fan harness that is wired in how the auxiliary fan was wired in. At this time both fans only work on high speed and with the a/c on. I do tow occasionally, but main concern is a/c performance and man did the fans help with the a/c. Ten times better than the clutch fan and auxiliary fan. That being said, I do keep an eye the cooling and trans temps especially when towing. Trans temps never get over 180. Since the upgrade I have only had one issue and that is because both fans come on high at the same time. The issue is the current draw when both fans turn on. Battery voltage drops briefly to 12.5 then comes right back up where it needs to be at 14. I know once i have the programming done this problem will go away.