I live in Germany and often use the autobahns. The autobahns in many places have no speed limits, so I suffered the same issue, as I also run 4.10s. I solved the problem with the use of the 22.5 Alcoa wheels. I have driven my dually right over the top of the alps, which was at times very exciting with the width of those roads, but that's another story. I was very concerned that the unsprung weight increase would have a devastating effect on my suspension, especially the ball joints. The wheels and truck tires work very well with no ill effects. I had to raise the front end 2" for tire clearance, which leveled the truck stance. I also had to use 2" longer front shocks to prevent extension slam on speed bumps. The effective final gear ratio dropped to about 3.68. I can run at 75mph at about 2000 rpm. The other added value was tire wear....it is virtually non-existent, because the side walls are so much stiffer. I was also concerned that the harder rubber would affect grip.....it didn't. They stick like glue. In point of fact, the rubber hardness was the same as the factory tires checked with my durometer. I can spin up the rear wheels in 4th gear coming up on the turbo in damp weather, but not with the Alcoas on. These trucks get their best mileage at 45 mph. As you go faster, the mileage drops off quickly no matter what gear or wheels you are running. These trucks are about as aerodynamic as an outhouse. The tires and wheels did not reduce consumption. In fact, they slightly increased consumption at lower speeds by about 1 mpg, but I can run the Alcoas at 75 and average 16-17 mpg, while at 45 I see 19-21 mpg. Although the wheels, wheel adapters and tires are not cheap, it does solve the speed issue and over time pay for themselves in less tire cost and associated component wear and tear on the truck. I think the gear or gear box alternative is more expensive and not easily reversible, where the tire wheel combination is. Further, when selling the truck, they can be exchanged for the original wheels and sold on separately. This way the net cost of this solution could easily be zero.
Steve

 

have the "brownie" 5831 in now. Gives a real nice overdrive , and able to kick down for the hills without loosing speed. Have not been able to shift smoothly all the time though. Seems to shift better without using the clutch. Anyone have some tricks to shifting nicely?