I use the Garmin RV GPS to make sure I stay off roads I am not supposed to be on. It allows you to put in your length, width, height, and weight and will check that against road restrictions. The only time it let me down was when it told me I could go through a road that had a low clearance bridge in Ohio, which luckily I saw online when reviewing directions! It also kept trying to turn me down a road near Natchez Trace in TN that didn't exist. The traffic feature also does some goofy study sometimes, but for the most part, I feel like it keeps me out of trouble.
I think the worst road we have done so far in terms of steep grades has been CO-139 while driving from Vernal, UT to Thompson Springs, UT. The speed limit dropped to 25 and there were several switchbacks that required dropping down to 15. I am pulling at 44' Fifth Wheel so it required a lot of concentration going around the turns but overall I felt ok. We were lucky to have a Pickup Truck that kept traffic pretty far behind us which also helped. Even with the steep grades down, the engine/transmission did most of the braking for me, and I only had to tap on the brakes to keep the speed down or slow down for the sharp turns. My best advice is just to not let your speed get away from you so you don't have to use your brakes.