When the temp got over 80 or so my rig sounded like a 1975 Ford 5 ton flatbed. The fan clutch would seize so it was spinning at cam speed. Ran fine in cool weather but when it heated up the engine power would drop and the fan noise would increase. I got a replacement fan clutch from autozone for 58.00 and it runs a lot better. This is how to replace it:
1. put a drain pan under the rig to catch the coolant and remove the lower brush guard to access the bottom of the fan shroud
2. with a cool engine open the radiator cap and disconnect the top radiator hose
3. unscrew the 2 bolts holding the fan shroud on. the fan shroud is in 2 pieces so push in the tabs to unlock it and it will separate. then remove the top half of the shroud
4. with a 10mm ratchet box end wrench pull off the 4 bolts holding the fan clutch to the water pump
5. put the fan on the new clutch
6. reverse the process to install and top off your coolant.