My 08 Tahoe has never been back to the UK since I bought it three years ago. So I drove it back to get things checked and see if there were any software upgrades needed.
All the fluids were fine except the rear transmission fluid which was dirty black. Not sure why this should be, but its been changed and hopefully won't happen again.
Apparently for the 08 Tahoe there are two software upgrades needed, and afterwards the truck appears to be running a lot smoother.
I checked the gas mileage on the way to the UK. Travelling at 70-80mph, with the odd spirt at 90 in Italy the truck averaged 12.8lt/100km, or 18.4 mpg US, 20.1 mpg UK. Returning I checked the gas mileage from Amsterdam to Athens, and I was down to 11.4lt/100km, 20.6 mpg US, or 24.8 mpg UK. This was travelling at similar speeds. It's a big difference, and would advise anyone who hasn't had their software upgraded to get it done.