Yeah, some of the early-90's Canadian made rigs were pretty hard shifting when the temps drop below freezing. Warming them up (driving 10 minutes or so) helps. I found sticking the rig in the garage helped, too.
Then you get a ham-handed driver (slamming gears) and it rounds the synchro for 2nd gear & maybe 3rd.
I was told switching to 40W oil in the tranny helps, but haven't had the nerve to try it myself.