Although it is very nice to have a GPS that displays or warns about low clearances, it is only a tool. Clearances can change due to road conditions.
So for planning purposes I use the
AITA Low Clarance web site for travel.
Now, here is another link where you can find just about anything for your GPS or Mapping program. I particularly like the MEGA file for MS Streets and Trips.
Have fun
Discovery Owners Club The MEGA file for MS Streets and Trips is a mind boggler.