I have enjoyed reading this thread and long ago decided to stay out of it, but Wolf Creek Pass encouraged me to share my experience.
Admission: I have never towed with a dual wheel pickup, so no comparison is intended.
But I have towed four different fifth-wheel trailers, each a different brand. That started 17 years ago. The last two trailers were towed over 50,000 miles each (still going on the last). I have been over Wolf Creek several times and Monarch many more times. I won't name all the passes I've been over but most of them in Colorado, including Douglas Pass.
I tow with a Duramax/Allison 2500 single rear wheel pickup 2007 model. With the tow/haul package I rarely have to apply the brakes on the descent. Once (do not do this at home) the trailer brakes failed and we had to come down Monarch with only tow/haul and pickup brakes. No trouble until a lady pulled out in front of us in Canyon City then slammed on her brakes on a yellow light. We did stop in time, but I will admit that was close. Remember--no trailer brakes at the time.
I'm not trying to prove anything to anybody. We are "recreational" RVers in retirement, not full timers, and make no effort to be expert in such matters. This is only to say that we have never experienced any lack of stability or control in a wide variety of circumstances over almost every contiguous state and even into Canada.
Good luck to my neighbor in Houston, even though I would not presume to give him advice.