I'm riding my usual daily route home from work, about 15 miles through downtown Nashville then South and into the rural roads. At about mile 10, there is a long gradual hill, about one-half mile or so, and traffic usually flows at 50 mph. Near the top of the hill, I start to lose power and slow down. I turn the accelerator, but the Buddy still slows down, just with more engine revs. It's a freaky feeling, especially with SUVs behind you, so I pull off the road. Everything sounds and looks as usual, and after a couple of minutes of pretending to check everything out but not doing anything I just get back on the road and drive home without incident.
So... everything is fine for a couple of weeks, but yesterday on that same gentle hill, almost at the exact same place, the same thing happens.

!
I am up and down hills all the time - never happened before or since. I drive the same road every day as a part of my commute. My Buddy as 12,000 miles, but the belt was replaced 3,000 miles ago. Could be a slipping belt, but it's not acting like a slipping belt in the traditional sense. Any ideas?