Just to stay on thread here my tranny downshifts a little hard too, but I don't think there's any problem. I've driven buses where the tranny was about to go out and everything felt loose on them. I know nothing about trannies, but when I worked for a big school district the last several years I probably drove 30 or 40 different buses in a year. Every bus felt a little different. Some made groaning noises when they shifted which didn't sound healthy to me.
The temp gauge: I have no idea what the bottom number is. I'll check tomorrow. I spent the first 200 miles trying to decipher what the gauge was for