Get yourself a Garmin Nuvi unit, ours is very reliable and you get free updates. It is used by all the volunteer search and rescue members in Montana, other makes do not have the accuracy that the S&R people need when out trying to locate someone.
Ours has never lets us down except once, and that was operator error
I transposed 2 numbers on the address we were looking for, but the Garmin took us to the place I told it to,
You will not be sorry. Also, it has never put me on a road where underpasses were to low for the mh.