Tom and Gail I use the same philosophy when I am using CC. Steep hill coming up I use the go peddle a bit to get a run at it. If I am losing speed to fast I drop it out of CC and manually operate it so it doesn't drop into drive at a high speed. That usually gets me an over boost check engine light for the next mile or two.
. For my older rig if I am going down mountain pass etc I take it off CC and use my exhaust brake as much as possible. It is not a real exhaust brake as I am using the fast warm up valve but it does keep me from having to ride the brakes. I wish I had at least one more gear in my tranny.
My old Ford holds very steady in CC and my tranny is capable of towing in OD with no problems. For the most part it also has plenty of power with the modifications that I have done over the years to it. It will overshoot the set speed by about two MPH before it settles down to the correct speed but only on real steep hills and I can live with that as it is more steady than most people driving by the peddle. It is usually about two/three MPH before it drops a gear which I watch quite closely. For most moderate hills (AKA Freeways) it just stays in OD and the boost spools up to maintain speed. I just watch the EGT's and let that dictate if I need to drop down a gear or let it ride in OD. All in all the old 7.3 four speed tranny performs fairly well. I do wish it was a bit quieter.
Tom Marty