The thing I like about Delorme is the ability to add in and/or modify an almost unlimited number of POI (point of interest) files. They let you customize the maps to almost any degree you want. You mentioned low clearances - there's a POI for that (from
lowclearances.com) that shows those places you don't want to leave an air conditioner. What the software doesn't do is plot a route to automatically avoid those low clearance points. But if you spend a few minutes with the software you can easily spot the problems and reroute.
al