Alright, I'm pretty sure we have pinned this down to the radiator. When I drove the truck a few days ago, I had a pretty considerable leak from the bottom what I assumed was the rad, but wasn't 100% sure. Before driving the other day, I bled the system. This afternoon I bled it again before adding K-Seal. The rad ended up dropping 3/4 of a gallon of coolant in just one hour (15 min driving)

I brushed out the radiator, and added the K-Seal. The first 10 minutes temps reached 210F... after 15 min or so the leaks stopped, and temps dropped down to 199F...

Let it idle more, and took it for a 15 minute drive.... Temps were at a solid 201F minus turning around, when it hit 203F.

Brought it back to the house and let it idle. Temps went up to 221F after about 10 min of idling, so i turned the heat on high, and temps dropped back down to 204F when I killed it.

I'll top off the coolant tomorrow morning, and we should be good to go. For now anyway.

My only question is why would temps reach 221F when idling after the drive? 215F I could see, bit not sure if the rad is the only item left to deal with.

 

The engine gets hot while driving, and the rad has to carry away that heat, which takkes time. The air flow has degreased from 5280 feet per minute to more like 800 feet per minute with the fan. The viscous clutch may not be coming back top full power if rad is partially clogged. Plus a clogged radiator can cool off while driving, but just can't keep up with lower air speed. Turning heat on high did not increase coolant, because unlike models with a heater valve, the D2 has heater core flow all the time. What did happen is that the surface area of the heater core had air moving across it, and that makes me think your rad has sludge. You can test it with the Mark I palm reader or an IR thermometer, top to bottom, warmed up, engine off. Should be within 10F. Colder lower section is no or reduced coolant flow.

 

looking at your video I would have to say you need a new radiator, if you can see threw the fins then they can be dissipating heat.
also by the looks of the cob webs on your evaporator fan motors I'm guessing there are not running either.

 

Yep, you mentioned a few posts back that electric fan wasn't coming on. Need to fix that. And those gurgles you hear are air in the cooling system or exhaust gas. You can purge the air with the bleeder T, but exhaust gas will keep coming back if head gasket.