I have driven a D24T through the Rockies and it also struggled above about 9000'. It moved OK once it was rolling but getting started from a dead stop was a slow and smoky affair.
I think for high altitude operation a VNT setup would be the only thing able to get things spinning early enough in the rev band while still allowing enough airflow at the top end. Even for a regular station wagon when the air is thin the engine just bogs at low RPM when trying to get moving up a hill. I can't imagine how it would be trying to haul an extra couple thousand pounds of truck.
What kind of gearbox do you have in your Pinz? I've had both automatic and standard shift Volvo turbodiesels at high altitude and the automatic was much easier to use with the engine in its compromised state, since the TC allowed enough slip to get the engine speed up high enough where the turbo started to help when moving off. The manual shift car was impossible unless you slipped the clutch. If you have an automatic or some kind of low-geared standard gearbox that allows you to get the engine wound up right away, then a larger turbo would possibly help but at low revs you're just going to have that much more air to move and you may be trading top end power for low end response in a big way. (As you know these have plenty of lag even the way they are stock!) Seems like a VNT is the only way to have it all.... I got one off a Jeep Liberty CRD and had ideas of putting it on my manual trans TD wagon with a mechanical/vacuum control system but decided to live with the automatic instead. Some of the Mercedes guys have had good luck getting VNT setups to work on their old diesels though, so it should be feasible on a D24T as well, and on those Benzes they are getting instant spool off idle, lots more power all through the rev band, and even a few more MPG as well...
Last time I was in the Denver area I stopped by a place out in Golden called LinDen Engineering, it was near a biodiesel pump I was using -- they had a handful of Pinzgauers parked there and one was a diesel. Would that have been yours?
