So I took your collectively excellent advice to heart and ran thru a bunch of different things. The upshot is that everything checked out fine with the exception of the fan clutch -- which was worn and loose. So we replaced both the clutch and the fan with new Isuzu OEM units. This was several days ago. Ambient temperatures have been running in the mid 80's as opposed to the high 90's of two weeks ago. This makes it a little hard to tell. But I've not seen the engine temp gauge rise over the midpoint and I'm hopeful that the issue is solved. Again, thanks so much for the great feedback and also for the sense of community. Nice to know that there is a group of us committed to keeping our unique little VX beasties up and running for the long haul.