I'm off I-20 in Kaufman Co. They just recently lowered the limit to 60 on this stretch between Dallas and Terrell. It's a training zone for the HP....and they get lots and lots of training!
I drive Dallas to Shreveport about once a month, but I use US 80 out to MP 500 and pick up I-20 there. The limit has been 60 or 65 on the US 80 and even part of I-20 for several years. I rarely see more than one vehicle pulled over anywhere.
I drive a 1995 Toyota 4WD pickup, 3 liter V-6, manual 5-speed, 113,000 miles. For years I drove 70-75 on this run, but since gas passed $2, on the last couple of trips I tried to hold 65, hard to do exactly without cruise control, but I'm now actually seeing 20 mpg rather than 18.5. I have replaced the cat converter with an aftermarket one that probably causes less back pressure, and it also got me through the Dallas area emissions inspection with a much better score than last year's squeak-by with the original stock one.
My trip now takes me 15 minutes longer, but if I start 15 minutes earlier, it works out the same, right?