Driving 5 mph under the speed limit in the dark on a winding road seems pretty reasonable to me. Do you have deer out that way? 5:30 AM is prime deer hitting time!
I’ve never seen a deer on the stretch of road I mentioned I suspect because most of the lake bank is steep. It isn’t reasonable. The road could actually be driven safely at 55 mph but there are intersecting streets to keep it down to 40. But that’s not the point. These are the same idiots that do it on the freeway in the left lane as well. They are oblivious to their surroundings and become a hazard unto themselves. If they are that uncomfortable they could pull over in the numerous pull over spots and let the traffic buy. RV owners very often extend that courtesy when they know they cannot keep up nor desire to keep up with traffic.