I feel really badly about your experience, but I don't want to dissuade anyone who might be reading this from getting a Fargo. I have a garage full of really, really nice bikes (5.5, 9.9, 720, Blue Ridge, etc.) and all I ever ride anymore is the Fargo. It's really a fantastic, versatile, comfortable thing.
I have the front and rear Nice Racks on it, plus the cable tie-on baskets from Rivbike, and routinely load up the bike willi-nilli with all kinds of crap (firewood, cases of beer, flats of pansies) and it handles just fine at ~25mph.
That said, the idea that you'd have really big wheels, really big tires, a frame made in some cancer inducing sweatshop in Taiwan, and the panniers would shake on a 40 mph downhill isn't a total suprise. The Fargo is really a gravel road and gravel trail bike - it's not a loaded touring bike. If you're planning bombing down mountain switchbacks with loaded front panniers, you want something like a Co-motion Americano, with smaller wheels, made in USA, not a Fargo. Or really, you want a B.O.B. trailer. (The Fargo and the B.O.B. carry a tree just fine, by the way).
PS - please come back to the U.S.A on another trip. We'd love to have you, we need the economic boost.