I do not drive a truck that is speed limited, but I can tell you that you will rarely see me going over 60mph........
for starters it is just as you stated, most trucks are goverened at 63-66mph and I have found it is just easier to let them pass me than me have to leep skipping around them.
Second, the difference between going 65mph and 60mph is litterally NOTHING in the big picture. Unless you are traveling 700 miles NON-STOP then you will arrive say 20-30min before the guy going 60mph. Now I know most you guys in this forum don't have to pay for fuel, but that extra 5mph is also costing you .5mpg, which calculated can avg between $300-$400 a week.
Lastly, you ALL need to realize that everyday some new A-HOLE just got a license, weither it be a 4wheeler or a CDL, and they all are always in a big hurry to go nowhere.
So just sit back and enjoy the ride........ things could be worse, you could be stuck in a cubicle typing on a computer for an endless and thankless job like the other 70% of the country.