It would be really interesting to see one of
the owners clubs, internet forums
or diesel pickup magazines
do a multi-truck Convoy-style fuel economy test
(SAE/TMC Type 4)
on the various model years of Cummins Ram pickups.

Ideally,
the test would first be done unladen trucks only at 70 mph,
then repeated with each truck towing the same model and weight U-Haul trailer

I would bet on the
early 1998 12 valve 2wd
as being the MPG champ,
but I have always thought
these '98s would do even better
if they had the 3.06 ratio Dana 61 diffs like some of the earliest had.

http://en.wikipedia.org/wiki/Dodge_Ram

Some years ago after Hurricane Katrina hit New Orleans
many diesel pickup owners were hauling the exact same FEMA bought trailers from the Elkhart Indiana area down the same interstate routes to NOLA
and the Dodge, Ford and GM pickup owners
were exchanging fuel economy results.