Larry, You've gotten good advice, I think Charlie is spot on about the TH mode issues. I tow a a heavy 5th with a diesel RAM 3500. I switch TH on/off frequently while driving as the needs changes. I'll run the cruise on when on the level roads but as soon as get into the climbs (live in Santa Fe and drive the rockies), I'll switch the TH on. With the diesel I use the exhaust brake to do much of my slowing down and will down shift to keep the speed down on the downhills coming off a mountain pass. I'll frequently drop 5,000 ft. and only touch the service brakes a couple times all the way down. Always start out slow on the top of a downhill, you can allow speed to grow if deisred, but burning it off can be a white hand experience.
The idea to train with cones in a parking lots is right-on.
A couple of things not mentioned so far is that I always try to keep a mental note of the traffic behind me and on my sides. Right now I don't have a rear view camera, coming this spring, so I want to know what is back there. A semi can be totally hidden behind me, not to mentioned little cars. They'll pop out of the hole without warning, just as you are preparing for a lane change.
If you are doing a left turn in a multi-lane turn, always use the outside most lane to give yourself a longer turning radius. May need to modify if this would require fast lane changes for another turn. I try to maintain more space between me the the vehicle in front for increased braking times. However, in a busy are folks will cut in front of you all the time. Perhaps giving you only a car length or so of space- yikes.
I like to take frequent rest breaks to stay alert.
Be safe and have fun in your adventures.