Annnd... this is beginning to resemble "thread drift".
Yes, of course the tiny 5.9 is pathetically under-sized/powered for 38,000 pounds going over the Sierra Nevadas and such climbs.
On the other hand, it gets us there, and the downside is only that it takes a couple extra hours. Well... and creates a traffic hazard.
I keep toying with the idea of a larger engine. Of course, I would have to find it at a "highway robbery" price.
And a big stick-shift transmission.
And the REALLY cool thing to do would be to install such an engine under the floor, like the old Crowns. Cummins does make "horizontal" versions of some engines, such as the L10 and M11. Many of these were sold to England. But maybe a normal vertical engine can be converted with a few parts that can be bought over the counter?