We have a Garmin but they keep changing their model numbers and pricing so I can't tell you much about what they have to offer today. As long as you keep doing the updates the maps of all of NA including Mexico are about as accurate as you can get.
As a former trucker and now 11 year full time RVer I can tell you something about low clearances - there is no GPS or list or anything that will tell you where every low clearance is. I know of several specific low clearances that appear on no GPS or map or list I have ever seen - and I look. Low clearance aids do have some use but if you count on them and not on your own eyes you will have problems. The only way to be sure to avoid low clearances is to stay alert and pay attention at all times. Try this - GOOGLE - On The Road To Success There Are No Shortcuts - the picture is real - a professional driver - I know the bridge - it is not on any list or GPS.
