Mexico maven "Mexico" Mike Neslon, renowned travel log writer for Ssnborn's insurance for many years, is retired but still on the road, still blogging at https://www.mexicomike.com. On his latest foray, he found some nuances pertinent to the Gross Vehicle Weight Rating* (GWVR) listed (or not) for your vehicle. Essentially, if you have a 3/4 ton pickup or larger, you need to closely read this.

He was at Ciudad Reynosa, Tamaulipas, where he interviewed two Banjército (Army Bank, where you must pay for and get your receipt prior to securing your auto permit) officials about this issue. He had earlier interviewed two Banjército officials in México City, but he wanted to determine how this actually worked at the U.S. - México and Guatemala border (very likely applicable at the Belize border as well).

"It is official. Unless your title or registration shows your vehicle is a motorhome, you cannot get a temporary import permit (some call it a TIP) for a car/truck with a GVWR greater than 7,716 pounds. No if's and's or but's (sic)...

However, if your state's title does not show GVWR, but only Vehicle weight, an official smiled and said that was all she would see. So there IS a loophole, albeit a small one. It does not matter if you have a camper in the bed or your truck or not. They only care about what the title says.

This explains why some Sprinter and other camper van drivers had their application for a TIP denied. Their vehicles were listed as passenger vehicles on the title. This also explains why some people are having no problem driving an F-350 and towing a trailer. Their states don't list the GVWR. I did specifically ask if a truck pulling a trailer was treated the same as any other truck and it is."

Mike's page on how to proceed to secure a car permit for México import here: https://www.mexicomike.com/livebetter/car_permit.htm

He also says: "Don't Get Your Vehicle Permit Online
While you can get your car, truck, RV or motorcycle permit online, I don't recommend you do so. You still have to stop at the border to get your immigration permit, so what's the benefit?"

*The gross vehicle weight rating (GVWR), or gross vehicle mass (GVM) is the maximum operating weight/mass of a vehicle as specified by the manufacturer including the vehicle's chassis, body, engine, engine fluids, fuel, accessories, driver, passengers and cargo but excluding that of any trailers." (Wikipedia)