martyllian, my hch does this too when i restart the engine after FAS. Except, my car's "bucking deceleration" is not nearly as bad since I was only going at 35 mph. (felt like shifting from D to S gear at 35 mph on a downgrade).

I guess from your description of "long, large hills" that you may have been going at a much faster clip when you turned your engine back on - the faster the speed, the larger the "bucking deceleration." I'd recommend not turning the engine back on unless you are at 40 mph or below to be more gentle to your transmission and not experience such a harsh "bucking deceleration."

on another point - i sometimes have to drive on steep descents, and i'm afraid to use FAS there because of how quickly power brakes might be used up. Are non-powered brakes sufficient to brake a car down a hill, or do you just have to push harder on them?