Well, when things get bad, i prefer to pull off if I have any doubts in my ability to keep things under control. Often, when things start to get slick, I feel comfortable slowing down and staying on the road. Other times, especially when wind is involved, I just don't think it's worth the risk.
Whatever you do, DON'T EVER let other drivers, be it 4-wheeler or otherwise, try and intimidate you into driving "their" speed. You drive ONLY as fast as YOU feel comfy doing; they'll just have to wait. Remember, THEY aren't going to be paying the bills if you pile your truck up. Furthermore, they won't pay the medical bills for you or anyone unfortunate enough to be involved in an accident, nor will they likely employ you if you lose your job due to said accident.
Somewhere along this thread, I think someone will come on to try and tell you not to set your trailer brakes...