There is a factory software update for the 03-04 models to solve overheating conditions. My understanding is they updated the fan speed controls for 05+ and this software update brings the 03-04's up to date. Ive been wanting to have mine done for over a year but havent gotten around to it. If you go to this web address and put in your VIN it will give you all the updates that are available for your truck.
https://tis2web.service.gm.com/ The 1 for the fan clutch issue is listed under PCM/VCM Control module. It gives you the part numbers and everything for the updates. Mine (also an 04) came up with 4 pages of available updates to all kinds of functions....But the main 1 I was interested in was the overheating problem. The 1 for updated shift points is probably a good 1 as well. Im going to try to go ahead and get these done soon.
Im still unable to find the detailed article on diagnosing the fan clutch but if you look at the service manuals listed on Moosemans profile there is the original diagnosis papers listed under 04 engine cooling that should provide a little more understanding of how it all works. You do need a shop quality scan tool to go thru all the steps however. Ive battled this problem for 2.5 yrs and think I solved it now by installing an original BEHR factory fan clutch that came on these cars. The 1 have on it has over 200k miles on it but it has worked properly although Im still a few weeks away from the 95-100 degs days that will really tell the tale. Drove it today with temps around 89 degs and needle held firm at 209 the entire way. I still run my electric fan at stop lights and bumper to bumper traffic.
Another thing you may try....i pop my hood and then click it down but dont completely shut it. Leaves about a 1" gap in the front. Yea Im scared to death my hood is going to fly open if i hit a railroad crossing or a big bump but so far so good. I dont know if this helps at all, could make it worse i guess but its something to try as we're grasping at every straw...