Hey guys,
on the other side of the Atlantic river you are tough on speeds. We in Europe have the ETRTO, which is simelar to the tire and rim in the states. The ETRTO gives on the tire side wall a load index and a speed index. Military tires are useually good for F or G in speed index, which means 80 or 90 kph or 50 /56 mph. You can ad a little speed with the propper tire pressure plus 10 percent. Overload you can compensate with a lot higher tire pressure.
So far the tire side.
The next is: It is a MV, which is designed for speeds less than 60 mph. Why you want to run it at 70 or 75 miles per hour? You have a MV, so I think you must live with the rules of MV. Else to my understanding you should change to the civy truck sceene.
In Europe a truck over 3.5 t (7700 lbs) legally is allowed a maximum speed of 80 km/h (50mph). So tires for us are not the problem exept to reduce engine rpm for fuel consumption reduction.
Wolf