Arkansas did have a 75 mph speed limit before the National Maximum Speed Law kicked in. So technically, they raised it back to 75 mph..
I was about to say something on that and then saw this post. As a kid, our family drove the I-55 segment from IL through AR several times and it was always 70 in IL and MO and bumped up to 75 in AR. There were ominous supplemental signs in AR under the SPEED LIMIT 75 signs reading "NO TOLERANCE". I remember driving it with my mom and still having my IL learner's permit, and keeping a nervous eye on the speedometer, even though there would be occasional vehicles skipping by at 80. I figured out-of-state plates, young kid, 76 gets you popped.
Then, across the I-55 bridge in Memphis, it opened up pretty quickly to 75 following the hairpin ramps of the Crump Blvd. interchange, and I was surprised to see an urban speed limit posted that high. Didn't last long on a trip as we were soon in MS and back to 70 mph, and you didn't want to push your luck there either, with out-of-state plates from the north.