Silly me almost paid for a Quickchange differential to be installed in a 1995 Ram.

$1400 plus $1100 installation about the year 1999.

Quickchange and 9” Ford are cousins, if I remember correctly.

Like an itch ya just gotta scratch,
I wanted to know how engine rpm and throttle opening
affected vehicle MPG, engine Brake Specific Fuel consumption, and acceleration.

I probably would have done some quarter mile runs with different ratios and 0-60 mph runs at Rockingham.

I could have further amused myself by towing different loads up my favorite steady 4% grade hill.

This might all sound crazy
but there is an old SAE paper from a British group
that took a vehicle,
fitted two Laycock overdrive units in series
behind the 5 speed manual transmission,
and drove around collecting a huge amount of on road data
that they condensed into interesting graphs of
speed, engine rpm, manifold vacuum, fuel economy, etc.

The two added gears on the Quickchange diff do add their own increased friction.