I wonder if Cummins will make public a BSFC graph for the new 2.8 I4?
In the past Cummins was one of the few engine manufacturers willing to publish those.

There are a number of now very cheap
1994-1995 OBD-I 2nd Gen Ram 2wd pickups
with the uninspiring 3.9V6/manual powertrain.

With a 2.8 I4 Cummins repower such a shortbed Ram might be able to get
Over 30 MPG at a steady 70 mph
on a level nearly windless blacktop Interstate.
On a BSFC graph the
“island of best fuel economy”
would need to be about 0.3 lbs/hp-hr or lower to get there.

In many states the OBD-I vehicles are no longer emissions tested.