Have a garmin 2597 for regular use and a garmin rv760 for my travels. Both are the same unit but of corse the RV unit calculates your height and length into the route and helps avoid low bridges.
As stated above the RV760 can take you down longer routes to bypass low bridges. In some cases it is merely the RV760 not knowing the height of bridges. One item I like it does have a ton of RV related preloads, ( you can update the 2597 with the same), and will give you about a mile warning of sharp turns.
Over all I like it.