Marvin is right about the POIs from the Discovery Motorhome web site. I use them but there is one caveat: they are not regularly updated like commercial programs. Having said that, how often does a bridge clearance change?
There is a commercial program designed for larger vehicles (truckers). Co-Pilot has a version for trucks that takes into account truck routes. Go to
http://www.dieselboss.com/Travrout/mapping.htm. That web site also has a smaller automotive-type GPS that's programmed for truckers.
If you're really into it, the site has rest stop listings, diesel prices, laptop mounts, other software, etc. I'm not endorsing the site but it's a place to start.