5W-30 should be okay if the truck has a block heater. This diesel truck coming up the Al-Can MUST
have a block heater!
If it's much below zero, plan on staying at hotels with bull-rails (pull-up-to railing with 120 VAC outlets at each parking spot for vehicle block heaters, battery warmers, etc). Plug into bull-rails every chance you get. If it's below -15 or -20 degrees F, plug-in your vehicle and go out and start and run it every 3 to 4 hours (once in the middle of the night and warm it up). This is no joke -- especially if you don't know how it does in the deep cold.
Most hotels/motels in the bush have these bull-rails offered to their guests as a courtesy/convenience. But, it's best make sure though before laying down your money for a room! For that matter, plan on staying at well-traveled hotels/motels along the way. And this is most important: plan on stopping at a motel before too late at night! Most of the proprietors don't stay up all night long at the desk, nor do the bush gas station operators along the Al-Can distribute gas/diesel at wee hours in the morning. They're closed down!
BTW, most of those motels open through the winters in N. British Columbia, the Yukon, and the bush Alaska communities are well-traveled though. Please plan on getting fuel at every
town, village or remote fuel-up open along the way, especially north of Fort Nelson. Gas/fuel stations get might thin north of there -- especially in the wintertime! Bring along two new filled 5-gal yellow fuel jugs with you in the back of the truck (make sure they have good anti-gel supplement in them). You'll thank me if you run into a bind and have to camp out in the cab of the little truck overnight. That fuel will come in handy in order to stay warm and still be able to make it to the next fuel stop the next day. Sometimes those fuel stops can be 200 to 250 miles apart in the winter along the Al-Can -- several gas stations close down in the winter!
Moreover, take easy to make and eat or already prepared food, water, coffee, a small packable gas stove and matches for soups and stuff, paper bowls and plates, good sleeping bags, parkas, insulated gloves, long-johns, warm hats that cover ears, light snow-pants, and layerable fleece. God forbid you breakdown. It could be hours before someone mosies along!
Drive on no less than snow or A/T tires that have the severe snow service rating. You'll be driving through MOUNTAINS in the winter. The N. British Columbia Rockies and further north can be a pain-in-the-backside to drive though if there's a recent snow or if you're caught in a storm. This is especially the case if you're not used to driving on snow and ice conditions. Watch the weather forecasts each day for the road ahead -- ask in the towns at the motels, gas stations, and restaurants what the weather is like for the day or next day. Bring a properly inflated full-sized spare tire. Reinflate the spare in the cold weather along the way, for it will lose much pressure as compared to the warmer, Lesser-48 states.
And for God's sake, buy a 2019 MILEPOST
book! It will tell you what you need to know about the Al-Can Hwy and help you know what's ahead and PLAN for it! https://www.amazon.com/MILEPOST-201...s=milepost&qid=1578380127&sr=8-1
This is off the top of my head.... from someone who recently lived and worked in Alaska for 25 years, and has driven up and down the Al-Can Hwy 7 times -- two times in the dead of winter like you're doing! I still own a home in Palmer, Alaska, 55 miles NE of Anchorage.
God Speed! And please don't take my advice for granted. I could very well BITE you where you don't want it!
- a crusty old Alaskan that doesn't have much patience for Cheechakos! Look up "Cheechako"