Some notes on comments above based on things I have recently read or personally observed...........
The law allowing foreign fuel and stations into Mexico states that transportation of these fuels once in Mexico must still be done by Pemex - Foreign companies cannot transport their own fuel.
Even if Mexican trucks do not have the emission device to reduce sulfur emission beyond the 15ppm level of ULSD it would still mean a reduction and pollution and be beneficial to Mexico to get as much ULSD out there as possible.
Though I do see many US trailers in Mexico I have never seen a US tractor in Mexico - tractor being the "truck" that pulls the trailer. I have not seen trucks of any type built for the US market in Mexico. Only trailers. I have seen some very heavy equipment and specialized trailer hauling extreme heavy equipment but all with Mexican tractors doing the hauling. I have even seen equipment so heavy they connect two tractors together to haul it - but still two Mexican tractors. US branded tractors used in Mexico such as Kenworth (KenMex), Freightliner, International are all built in Mexico for the Mexican market. These US branded factories in Mexico do export to the US but those trucks are built to US specs whereas the trucks built for the Mexican market aren't so far.
This PEMEX website . . . http://guiapemex.pemex.com/SitePages/home.aspx#!. . . . provides the number and location of every PEMEX station - if you zoom in and click on the location you will get the station number. It will list the franchisee of that location with the address as well as today's price of fuel at that station. I see no info about UBA.
EXAMPLE from Guia Pemex

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Here's another located a couple miles south of Los Mochis - not mentioned is lots of safe truck parking as well as that the Comida Rapida listed is a Subway Sandwich Shop

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