So it is like -11 here with the windshield today, after driving for about 10 miles it start creeping over 210..220....230... and then I lowered the blade and slowed down my speed to get it under the 210 mark again. I did not make the change to the clutch as you mentioned in your above post as I had already had it installed.
Both upper and lower hoses are at temperature as you would expect, the radiator is flowing really well, so I guess this is really got to be a air flow issue. If the water pump was going bad internally, I would not believe I would see the amount of flow that I see when the cap is off. The line from the heater core to the radiator is flowing a solid 7/8 stream like no other.
The outside temp does not affect the fan clutch. If the radiator temps go above the temp that the clutch is set to engage, then it will engage..... it's sitting right behind the radiator. Do not mess with your clutch. It should work properly out of the box and needs no adjusting. If it's bad out of the box and you F with it, your warranty just went up in smoke.
Now, couple things to check. When you get it up to 220-30*, pop the hood and feel if there is air blowing from the back side of the fan. (you should feel a ton of air being blown on the engine by the fan even at idle) if it is than your fan clutch is locked, also when you rev the engine up at those warm temps, you should be able to hear the fan roar. If you can't hear it roaring at all, it's not locked up.
2nd issue. It's -10 where you are at. Thats flippin' cold. Lets keep in mind something, your truck is designed to stay below 220* in 100* heat, with the A/C on, while pulling a mountain pass. Snow plow or not, you're cooling system should be able to keep up without the fan even hardly having to come on in that kind of cold azz temp.
Find out if your fan clutch is actually working or not and report back. If it is, then I still say you have a stat that is only slightly opening or you have a defective radiator. The way to tell the difference there is when it is "hot" jump out and feel the bottom radiator hose. If it's cool to warm, then youre stat is not opening properly. If it's flippin' hot, then the radiator is amazingly not keeping up and is plugged up.