I wonder if a truck with 3.92 gears might actually engage the MDS more often. Yes the 3.92 truck will turn higher rpms at a given road speed. But because of that it also has more mechanical leverage, so less torque required to move the truck under similar load. And that might mean less need to bury your foot in the throttle pedal. Maybe?
I have 3.92 gears, and it will come on as high as 78 mph for me, but only in ideal conditions. It seems happier to engage at 70mph or lower though. I can also accelerate lightly at almost any speed it's engaged at, without it disengaging. Couldn't do that so well with my Grand Cherokee, but that had 3.09 gears.