I can hardly believe that someone pulled over for two hours. Not here.
You need to learn to stand up for yourself. Guess what they ask you after you slide off a snowy road? "If it was so slick, why didn't you pull over?"
Seriously, if you willing to risk a crash because you are intimidated by threats to keep driving, you need to contact a member of your safety committee, or the feeder manager and ask him or her, exactly, what you should do if driving conditions give you the feeling that you may crash. Have this conversation with your union steward alongside you.
If you think they get mad when you show up for the sort two hours late, imagine how mad they will be when the loads arrive 24 hours late, after they needed to be off-loaded to new, undamaged trailers.
You are responsible for driving safe. If that means you need to pull over for two hours or more until it is safe, well, that is what they are paying you for.