08 D16 fan clutch/temps Sensor?

Earlier this week while headed out on vacation with the family my 08 D16 started acting weird. (used to haul 5th wheel toy hauler)
On the analog gauge the temps started running a little higher than normal and the fan clutch wasnt kicking in until the gauge started hitting around 210*. Now normally it would kick in much sooner and the truck wouldnt run as hot. Mind you I am only pulling around 24,000lbs and no serious grades. Outside ambient temps were ranging from 85* to 100*. When flipping through the digital display of my gauges, I noticed the coolant temps were off 30* to 50*. So while the analog gauge showed 180*ish the digital side showed 145* (this is while running 65mph rolling down the highway. And at times I would see 201* on the digital display while the analog side showed 185*. My concern is that I am headed back to Las Vegas with the temps around 115* and would prefer not to overheat and hurt the truck.
Thanks in advance!

 

Thanks KB3.
What I find strange is that it used to kick on MUCH sooner. Where could I find info on wiring in a switch for the fan clutch? Is that something that is sold as a "kit", or something I would wire in myself? I would just need to know where to find the "trigger" to kick it on/off as needed.
As for the cooling stack... I actually wash it out at least twice a year and I put less than 10,000 miles on it a year. I see it as preventative maintenance.
I made the our drive south this morning to get a coolant sensor from the dealer in Idaho Falls. When locating that, I found my coolant reservoir leaking at the bottom. And it looked like it just started. A quick repair back at the campground and I hope it can get me 4 hours south to the dealer in Salt Lake. Fingers crossed that it was just a sensor going bad.
Again, thanks, but some info would be greatly appreciated on a manual switch for the fan clutch

 

Thanks KB3! Did you fuse the 12v+ going to Pin19? I have 3 auxiliary switches on my dash that I have NO idea what they are for. I'm wondering if I can re-purpose one of them and just use the 12v out to Pin19?

My reservoir held up and almost got me to SLC before it started leaking pretty bad. Topped it off with some water just to make it to the dealer.. Grabbed a new one at the dealer, swapped it out and made it home that night. Truck ran a little warm on the way home, but average temps were 95-110 outside.
Now my water pump is weeping... Does the fan assy need to be removed to replace the water pump? It loos like I may be able to slip it out without removing the fan?

Thanks again!!

 

Thanks again KB3!! Greatly appreciate the info!