People do have to realize that GPS maps in Mexico are not quite up to those in Canada & The US. You shoudl not entirely rely on them as they can tend to take you down streets that are hardly RV friendly. Unless you are traveling with somebody who knows a particular town, it is best to try and check it out first on a bike or whatever or follow a bus through, especially if you have a large rig.
Google street view has mapped a very large portion of Mexico, including city streets. I have passed their cars several times over the last couple of years. If my route is goign to take me over unfamiliar territory I will bring up Google street view and follow my intended route using that to make sure there are no issues.
Even if the route has not been street viewed, viewing it from above using Google earth can work. Last March the road from Melaque to Puerto Vallarta was washed out by an unusual March storm. I had a caravan to get over that stretch and it looked like the only alternative was a 2 day detour up to Guadalajara and back down to PV. I went onto Google earth and saw a 40 km long secondary road joining the Melaque-Guadalajara road and the Guadalajara-PV road. It saved hundred of Kms. I followed it using Google Earth and it looked OK. So I took 10 rigs, some of them large Class A's over it, sight unseen. It worked out fine and the scenery was breathtaking. Plus we got to visit the birthplace of Carlos Santana.
Great post! Very helpful.