As has been noted, much of the blame lies (but will never be placed) on politicians who set artificially-low speed limits in so many places that speed limits are widely ignored even in those cases where they are necessary.
That having been said, a driver's logs should indicate whether he has a habit of speeding. No need for speed-restricting devices.
I don’t think it’s really safe for one of these trucks to go over 60 mph in any circumstances. The maximum safe speed for these vehicles is a good deal less than the maximum safe speed for many other vehicles. Not only are they filled with explosive material that makes a crash a lot more dangerous than crashes involving other kinds of heavy cargo trucks, but the tremendous weight of the liquid fuel makes for a long braking distance.
I was about 1/2 mile away from the White Plains, NY propane tanker crash in 1994. The driver apparently fell asleep and hit the concrete support of an overpass. The exploding tank turned into a missile, flew 300 feet (in my direction), landing on a house full of sleeping people on a residential street. It sounded like a huge bomb had exploded, to people at least a mile from the explosion site. Several houses were burned down, and 23 people injured, included a 30 weeks-pregnant woman who was severely burned (as was her husband), and whose baby had to be delivered by emergency C-section and reportedly suffered some brain damage as a result of the trauma to the mother and/or the premature birth. Many of the residents of the block have experienced lasting psychological problems (post-traumatic stress disorder). There’s no way a truck loaded with groceries or building products can have this kind of effect, but fuel tankers are in a category of their own.