I have the Garmin 770 RV, also.
Though, lately, I think I prefer using Google Maps.
The real-time updates have come in handy. We have been re-routed around accidents and road closures several times.
Using both simultaneously is the ultimate, since GMaps doesn't have the height/weight function, you could get re-routed to a bad route, but with the 770 able to auto adjust when you force a route change, it can adjust pretty quickly.
Going through the Wilkes-Barre/Scranton area last year, Google Maps warned us of a crash, and re-routed us, but the re-route took us into an old town area where streets were less than roomy, and clearances were questionable. The Garmin then showed us the way out of there, and back to RV friendly trails.