Just did Mexico to Belize.
My Garmin 2610 did great but the key is that you need to upload the right maps. I got a special map on Mexico that I downloaded from the internet. I was told the Mexican government site has the best GPS maps but I never found them. The Garmin world map is fine on the main roads but has no city streets. It was useless in the cities where you need it the most. Mexician cities have almost no highway markings and the logical way is not always the right way.
Plus you need a 2 GIG memory card to put all the maps into the GPS without taking out your USA maps. I found the onboard 2610 USA maps to be a joke so I also have the Garmin USA map in my computer.
If you don't go into cities your OK. But the cities are hard to avoid and as I said not well marked in any language.