[Mikendebbie]

I bought the 660RV a year ago - I think - for $199 or so...I think???
It was much cheaper than the 770RV which I think was $399 at the time.
I bought the 660 because it had built in traffic info received from a local source via FM signals (I think.) The 770 required me to be hooked up to a smartphone to receive traffic and weather. I wanted phone bluetoothed to the truck system - not the Garmin.

The 660 does have low clearance warnings. It warned us to re-route on one of the interstates in Memphis to avaid a low clearance bridge. Last year while I was doing research I believe I read that Garmin does not have ALL the low bridges that exist...maybe the ones on big highways.
I looked at the 780 page on Garmin.com - seems like the 660 has all of that same capabilities but smaller screen.

My new truck has apple carplay and I really like using the google maps app with it set to "satellite" view (not maps view). That gives you a real world pic of parking lots and fast food restaurant before you pull in and can't back out! I will still use the 660RV in addition to the google maps or the Chevy built in nav.