I10 has some 80mph postings east and west of Junction.
The fastest part of Texas,I know of, is state hwy 84 between Rosco,Tx on I20 and Lubbock with a little speed bump at Post,Tx.
A friend of mine had spectacular seats at Jones stadium at Texas Tech in Lubbock and he would give them to me several times a year,because he mainly used a luxury suite that was owned by one of his friends from college.I could put my Navigator on cruise control at 110mph and run it that way from Roscoe to Lubbock,only slowing down at Post, and you may not believe it,but would get passed by 50 to 60 cars going faster than that every trip.Sometimes 4 to 10 car groups. On those Saturday mornings all law enforcement for miles went to the games for traffic and make a showing at the games.Saw some wrecks sometimes where the cars would go out into the cotton fields a couple hundred yards before they came to a stop.