I have searched high and low to find a similar problem with no luck. Truck is at mechanic's shop now. Here's what's going on, need some help to diagnose.

Truck has 170k on the ticker and is a 06. Been monitoring delta for couple years and it reached 25 degrees last year so I had the local diesel mechanic install a new oil and egr cooler. Deltas have been around 7* since. Never puked one time since I've owned the truck.

So, to current situation, I was on the beach Saturday and truck got stuck. I had it in 4wd(I thought) and it was getting buried. Realized the hubs weren't locked after getting buried, rookie move I know. Got out to take off center caps and manually lock hubs. By the time I got back it truck overheat warning was on and temp was 235. I pull truck out of hole effortlessly and immediately park it and pop hood. Never anything but black smoke from exhaust and no smoke or puking under hood. Let truck cool for a few hrs and take off for the house, truck gets to temp fast and keeps climbing never going above 228 which was teetering on making the stock gauge move. The fan clutch does engage and come on at low speeds so I'm pretty sure it's working fine. It does not spin freely when truck isn't running, but it does spin with some resistance.

In trying to diagnose the problem I have noticed a few things. The heater will not blow hot air at any point. I don't know if this is related as I haven't used the heater since early March probably. The truck temp heats up faster than normal I believe with the temps remaining 25-40 degrees warmer than oil until about 200 where the oil catches up but remains cooler than the coolant by 10 degrees or so. I feel like it was always pretty close to each other while coming to temp until 185ish and the oil passed the coolant by 6-9*. The top radiator hose gets hot pretty quickly as engine comes to temp but bottom hose remains cool to the touch until 200+ ECT.

I pulled the hose off of the degas bottle that comes from intake to check for flow. Water doesn't flow at idle until truck reaches 200ish. Is that normal? Water pump was replaced 8/13.

I'm scared its HG but didn't know if that's possible without over gassing the degas to make it puke as it hasn't done that or had any puffs of white smoke or anything. I didn't have a pressure tester to check pressure but wouldn't it puke if over 16psi?

Mechanic said testing yesterday lead him to believe it was headgasket but doing more tests today so I'm assuming is wasn't definitive or any tell tale sign.

Could anything else I'm missing be the problem? In short, things I know tk be wrong are ESOF, heater, overheating without coolant loss. There was zero signs of overheating before the beach incident. Possible those three things are related at all?

Sorry for the long winded post, trying to be thorough.

Thanks guys,