I do not believe the 65 mph speed limit for semi trucks is law in the USA and as of today there is no mandate for speed limiters. Mandated speed limiting devices have been talked about for years but as of this moment there is no mandate. As of a couple of months ago a mandatory speed limit was in the federal rule making process but nothing came of it. We couldn’t even agree on 60, 65, or 68 mph. The trucking lobby continues to bring significant evidence that speed differentials between vehicles doing 80 and 68 would increase accidents on interstate roads.
Texas also did away with one speed for cars and another speed for trucks. I heard it was about safety also.