I just installed the RV770, and took the first trip with it last weekend. I agree with the OP, it definitely can map some strange routes, and give strange warnings. I've had Garmins in my passenger vehicles for many years, so I'm use to it's normal operation, but this one has some quirks.
I usually pre-map my route the night before just to familiarize myself with the route, cities, etc., usually on Google maps, and check the roads, bridges, obstacles, etc.. When I got in and programed the route in the 770, it planned a completely different route, so I don't understand yet how it's computing...
Gonna have to play with the settings and see if it get better.
2019 Redhawk 24B