Sounds reasonable, especially for the transmission. I suspect the engine is operating at a reduced "load" too, so that would account for the lower CHT. I keep a fairly close eye on my CHT and TFT and as soon as I start climbing even a gentle slope (more engine load) the CHT goes up a bit. On downhill stretches, even if not coasting, because some gas is needed to overcome wind resistance and maintain speed, the CHT will go down.
I'm a bit surprised at the reduction in your CHT though.
All these conversations almost make me want to regear my truck, since I tow with it. (You'd think though, that the factory tow package would have included optimized gearing.)
- Jack