Thats great that the trip went off without any major hitches!
I had the same altitude problem when I crossed the rockies with my 300D, actually had a number of issues related to altitude, smoking, low power, and the turbo lag became incredible!
Found this equation for HP loss at altitude for you, some of the problem could just be the normal naturally aspirated issues cars run into, especially an older car like yours-
hp loss =
elevation x 0.03 x hp @ sea level
1000
also a link-
http://www.wallaceracing.com/braking-hp.php
so if your car only has 60 hp base, you lost 12.6 hp at 7000 feet and got down to 47.4 hp. Whats the actual HP at the wheels for that car with the 4-speed? I know on the later 240Ds, they say with an auto versions, they have something like 38 hp, they would have been brought down to almost 30hp.
What does the fintail use for the ALDA or ALA altitude compensation? is it possible that this part is stuck or non functioning? maybe it worked partly, then got stuck as you decended later in the trip, especially if the car spent most of its life around sea level and these parts have never moved?