Truck Semi Tractor trailor
I'm in the U.S. speaking to people from Mexico living in the U.S. I need to say "I need a truck" and by that I mean a Semi or Tractor Trailer for moving freight cross country.
Usage varies across Mexico, but based on what I've heard used in various parts of the country, you can simply say "Necesito un camión trailer" and they should understand what you mean. In this case, "trailer" would be pronounced like "try-ler," not "tray-lur."
In the case that doesn't work, you could get by with "camión de carga" or even "camión de mudanza" (but that's specifically moving truck, different than what you want, I suspect).
Also, future reference: you can edit your questions to add more info. It's much easier to keep track of your question and all repsonses.
I hope this is helpful.
Being someone who has motorbiked extensively around Mexico, the sign engendering the most caution for me on vehilces is 'precaución, doble semi-remolque' which means 'precaution, double semi-trailer (unit)', i.e. a tractor unit with TWO trailers, a very long vehicle indeed to pass! So on that basis, I would look out for a semi-remolque if you only needed one trailer after your tractor unit.
Necesidad dee un gran camion o de un camion - trailer, para alguna cosa