RV in front of any number (760,660,770) equals big $ for Garmin. As mentioned many times you can't rely on the routing anyway.
I compared the RV-760 to a LMT-2797. The 760 gave bizarre routes and dead wrong turns in RV or car mode. The 2797 gave better routing and most other useful features at 1/2 the price. I would never trust a GPS to tell me where I could go and the routes based on inputting weight and length.
If you are operating a big heavy long rig you need to know where you are going before you start. No GPS is accurate enough to trust 100%. The Garmin disclaimer tells you that.