The route you take from Florida into Mexico depends on the type of drive you want through Texas. If you dislike Interstates, take the two-lane, black-tops. From Houston, take Highway 59 into the Texas valley and take either #281 or #77 south to the border to McAllen or Brownsville. Pharr has an easier crossing that McAllen. It's a slow, beautiful, drive through rural Texas, with things to see in every town and stop lights to make sure you see them.
However, the easiest way is to take the Interstates. It's a little further, but faster with safer driving. When you drive from Florida to Texas, stay on Interstate #10 through Houston to San Antonio. Do not take the Beltway #8, nor Loop #610 around Houston, but as you pass the Beltway, slow down, because radar is everywhere.
Follow Interstate #10 towards San Antonio and take Loop #410, south, around town, to Interstate #35 and towards Laredo. (Do not take #37 to Corpus Christi.)
In Laredo, Interstate #35 goes directly to Bridge #2 and across the border into Mexico. Loop around and under the bridge to get auto permits and visas. Entering Mexico at Laredo is easy but sometimes there are delays.
There is an alternative. About 15 miles before Laredo, on Interstate 35, is the exit for Colombia. It’s about 30 miles out of the way, but hassle free.
When returning from Mexico into Texas, always take the Colombia route. The crossing is empty, with very few vehicles in line.
However, the area is heavily patrolled for speeders.
For what it’s worth, Interstate #35, south of San Antonio,
becomes 75 mph speed limit, until near Laredo.
Check my website, www.LakePatzcuaro.org and click DRIVING IN MEXICO for more info. For info on the loop around to get permits click NUEVO LAREDO.
For info on the loop around to get permits, click NUEVO LAREDO below.