Look into opening up and cleaning your cooling stack out front.
Bugs, grass, debris can collect between the coils over time, restricting the flow of air to the fan clutch....which results in no heat detected and no full lock to cool down.
Peruse thru this thread, lots of pics of what kind of buildup you can find.
Spraying thru the grille at the car wash, won't do it. It needs to be opened up some to properly clean. https://www.duramaxforum.com/forum/h...l-install.html
2007 LBZ 3500 LT3 DRW Crew Cab, Sulastics, Putnam XDR 15K, B&W 30K-Turnover GN+Companion, Ride-Rite Air...EFI'd by Rob
2008 LMM 3500WT DRW Crew Cab, 8 'Flat/GN, Workforce Alum Toolbox, Ride-Rite Air Use-ta Haves 2006-6.0 3500 WT DRW ExCab Flatbed, 2005-LLY 3500 LS DRW Crew Cab, 2002-LB7 3500 LS DRW Crew Cab I Live my life in such a way that when my feet hit the floor in the morning...Satan shudders & says "Oh shit, he's awake!"