Tex Mex has a lot more cheese, sour cream, hard corn tortillas, hamburger, and processed products. Pork and beef are not cooked in pits or banana leaves. We live in a town where we have many authentic Mexican restaurants, thanks to the immigrant population. True Mexican food has limited queso use, which is mild in flavor, and crema as opposed to sour cream. Soft corn tortillas, lard fried tortilla chips. Chilis and salsa varying in heat, frequently cruda (raw). There are many variants of Mexican food in Mexico, much like regional food in the States. Think New England Clam chowder vs. New Orleans jambalaya vs. Florida stone crabs vs. Texas bbq brisket. Lots of different spices and cooking techniques. The Yucatan Peninsula, where we stay, has a differerent style than Veracruz, which is different from other places in Mexico. Fish, beef, pork, chicken, iguana, you name it!
Get a good authentic Mexican cookbook, the techniques and recipes are amazing!