We too have found most Mexican drivers courteous with an occasional exception of some hell-bent about to be suicide passing cars on a blind curve. I've seen less of that in the U.S. Truckers are sometimes slow in the hilly areas but they too are, for the most part courteous and helpful with signals.
Our recent trip was from northern CA to Lo de Marcos where we are currently. For anyone interested in a brief description, herewith:
http://garyrgruber.blogspot.mx/2016/01/northern-ca-to-mexico-with-stops-along.html
Happy and safe travels y'all.