Talking about mountain passes, something that worries me (and not sure it should), I pull a 4500lb frog behind a Cambria 30C class C, and leaving Centennial, Wy., going west up 130 Hwy, it was all the unit could do to make the pass. It was actually losing speed for several miles, and was grinding away in the lowest gear going about 25 MPH at it's slowest. I say "not sure it should" because I have never needed to stop to unhook. I've been up and down I-70 west of Denver several times, and it only gets worrisome going west up to the Eisenhower tunnel.
A car can be unhooked if need be, but what to you do with a boat if you can't make a pass? I guess you could choose your routes more carefully to avoid steep passes.