If you plan to drive a 3/4 or 1 ton pickup truck into Mexico, and obtain the Temporary Vehicle Import Permit sticker, here's something to consider...
According to "Mexico Mike" he writes this on his website: https://www.mexicomike.com/livebetter/car_permit.htm
As of May, 2016, Banjercito offices began denying permits to drivers of non-RV-titled vehicles with a GVWR of greater than 7,716.7 pounds.
The limit for a personal vehicle permit has been 3.5 metric tons for years. The weight limit used to be based on payload, but as of May, 2016, Banjercito officials began interpreting "weight" as GVWR (weight of vehicle + payload). I heard rumors of this, but I never believe rumors. So I personally went to two different crossings to ask Banjercito officials and got the same answer. That means no three-quarter or one-ton truck can get a permit. Most 5/8 ton Nissan Titans weigh too much (8,000 pounds). A Toyota Tundra generally does not.
If your title or registration does not show the GVWR, but only the weight of your vehicle (GW), you may be able to squeak through. Every state is different. Texas, for instance lists the weight and carrying capacity. Washington state lists the GVWR on the registration and a GVWR "class" on the title.
You'd think the officials would all know that a Ford F-250 or Chevy 2500 would be too heavy. I asked a Banjercito official. She shrugged and said she only knows what is put in front of her. However, at the Pichilingue ferry, the officials come out and look at the weight rating in the door of your vehicle. I am told they do that at the Guatemala crossings too. On the northern border, so far, they don't.
Some people feel more comfortable getting their vehicle permit online, which might be a good idea if your vehicle is too heavy, but your title or registration doesn't specifically say so.
My advice? Take another vehicle if you can. Try the online route. Otherwise, if you want to chance getting a permit (TIP), be prepared to be turned down at the border and sent home. If you are heading to Guatemala and coming back through Mexico, don't even get a vehicle permit online.