I've been driving a big truck for 6 years too long now and would have weighed in earlier except I hate phone posting.
Most trucks are indeed governed to somewhere in the 62-70mph range. Insurance companies give breaks for governed trucks, including independents. The governor in modern trucks is a setting in the software so the engine just quits pulling at the designated speed on level ground. Downhill, the truck will go as fast as gravity and the drivers daring allows.
Most carriers pay using cents-per-mile as the calculation. However the driver is also told what the mileage on the load is determined to be using a couple of different programs that calculate the distance between the originating zip codes and the destination zip. So really the driver is being told indirectly that the load pays him so much to do. Of more importance to a driver is the timing. Not only is he expected to be On-Time come hell or high water, being late can result in fines to the carrier and also result in the driver losing the next load and potentially waiting days for free for the carrier to find another one.
As mentioned, OTR drivers are legally required to use daily logs with e-logs being mandated for everybody this year. Local drivers may not have to use logs but a lot do anyway. A driver has 4 clocks, the 30-minute break within 8 hours, the 11-hour driving, and the 14 hour On-Duty clock, plus the 70 hour-in-8-days clock, all of which start counting down the instant the driver goes on-duty. So drivers hear the constant TIK-TOK in their heads as they try to get everything done they need to in a day.
Another thing, Due to the relatively poor pay, stress, isolation, and other factors the vast majority of drivers quit in the first three months and most of the remainder don't make it past the first year. What this means is that there's a very good chance that every truck around you on the freeway is being driven by somebody with less than a year's experience and probably less than 3 months. Further since tucking no longer pays well it doesn't draw from the middle class like it used to, it draws from the poor who tend not to have the social graces that were once more common and why you see these 500 pound slobs in flops, sweats, and stained t-shirt waddling around the truck stops and shippers.
