To successfully enter Mexico, please observe the following:
You must register your Carnet before departure at http://www.carnetatamexico.com.mx/ata/
Registration approval generally takes about three business days
Customs requires translation of the General List into Spanish.
All Mexican Customs ports accept ATA Carnets.
Carnet goods may remain in Mexico for six months. They must depart by the Final Date of Re-exportation on the importation counterfoil.
Carnet must be stamped in the last place in the US that you pass through before you cross to Mexico.
For example, if you are flying from New Orleans to Atlanta and then Mexico City, you need to get your carnet stamped in Atlanta at the airport CBP office. You don't need to pull your baggage.
You'll need to go back through security. Try to allow plenty of time for your layover.