Brian, first of all congratulations on the Tiffin, no doubt you'll enjoy yours as much as we do our Phaeton!
As for the Acadia, if it fits your family needs I would say go for it. We started towing a Dodge Dakota which with the bikes, tool boxes and various articles in the back came in at 4500#.
We have switched to a Saturn Vue which surprised me as coming in just under 4000# BUT, unless you look at the monitor you won't realize there's anything there, except in the mountain's then everyone wants more power. I've been across the Rocky's twice and never had any problems and usually can pass the transports ( but they weight double ours
With a toad of that weight you will need a supplementary brake system, the coach is engineered to stop its self but not an extra 5000#. There are several good systems and an article in the Forum library which will help with your selection.
With the truck I had an M & G Engineered brake system but it wasn't transferable to the Saturn so I installed an Air Force one which also works off the service air brakes on the coach.
I realize I have a few more HP and torque (ISC) than yours but under normal conditions I think you'll do fine.
Enjoy the trip.