I think you sort of guessed that you, at least, have a thermostat problem...almost undoubtedly. They 'fail safe' as in staying opened and will take longer to warm up and run cooler on highway or constant speed. Idling for 5 mins. probably brings temp back closer to center. Anyway, I've been through this twice and it's always therm.
On starts, just read today about someone with similar 'loss of power' and it was MAF for him...ymmv Maybe try to clean it carefully and at least eliminate that as issue.