I presume that you are going in to Mexico at Nuevo Laredo, 85 and toll 85D, at the City of Monterrey take the Periferico Northe going west towards Saltillo 40 and 40D that will take you to Saltillo.
Yust before Saltillo there is the cut off to Matamoros, you do not need to go in to saltillo, mind you this is a toll road, then you are going to take 54 and 54D towards Matamoros and 54/54D continues to San Luis Potosi, Queretaro, Arco Norte and Mexico City.
The designations 85,40,and 54 mean that the road is not a toll road, 40D, 85D and 54D means that the road is a toll road, all of these are four lane paved highways as good as what you find in the USA. you do not need to go to Linares, that is of course if you want to go there, all of the other roads are paved two lane roads the same as what you encounter in the USA, yes you can travell in your 5th trailer yust be carfull.
navegator