Jim has mentioned he doesn't frequently drive the Frankenheap on the highway, so his good mileage makes sense.
That is true, but the best mileage has been on tanks that included more freeway driving. That may have still been in the cobweb-clearing phase. Right now I drive so little that data points are a bit hard to come by. Also I have envisioned eventually taking the heap on cross-State trips, but it is not quite yet up to the required standard of reliability. (Everything needs to work perfectly and have done so for awhile, else my wife will be really nervous. Also I'd like to have the CC installed. And the trunk emptied of parts. And the rear footwell lakes cured. And and and...)
I've seen the other phenomenon also, my Dakota is a V8, a friend has a newer one with a V6. I was shocked to find we get the same mileage and sometimes I get a bit better. This surprised me because my truck has a buncha miles
Dakotas (and Durangos) get worse mileage than they ought to, it seems to me. Anomalies like that don't surprise me. I'd like to have a last-generation 4wd extended-cab long-bed Dakota with a Sprinter diesel motor in it. My wife would really like it, too. Perfect styling (to me), functionality, and fuel consumption system all in one place. Come to think of it, there's a _lot_ of vehicles out there that could be substantially enhanced by having a Sprinter diesel in them! -- Jim