When you start a post with "European Liberal," right away many of us will ignore the thread, or answer with some 'off-color' answers, believing a troll has arrived. If you are not a troll, and an actual European Liberal; great for you, but when selecting a name that you know will obtain remarks such as you received, is not too intelligent on your part. It doesn't take a brain scientist to understand this forum leans to the US conservative side of the political spectrum.
But, just in case you are not a troll, I'll answer some of your questions.
The 5-cylinder Isuzu diesel will be arriving sometime in Europe. Being an export, not sure exactly when, but it is a go.
The 4L70 trans is strong as hell, and the 5- and 6-speeds that GM offers will also downshift in the mountains. It not as much a problem with the trans as a problem with the HP and the weight of the vehicle.
The engine/trans combo does ok in the high mountains, but remember, you lose HP as you increase in altitude, so the '07 with more HP would be more beneficial, since I would guess the diesel will downshift quite a bit too. More torque, but at cruising speeds you are looking for HP, not necessarily torque.
Don't believe OnStar is available in Europe; not sure, so I would advise you to check first on this feature. I figure my fuel mileage and miles remaining based on the trip odometer and knowing a rough estimate of how much fuel I have, and I'm accurate within a mile per gallon or a few miles till empty. Easy to do these calculations in my head with my 4th grade education.