1) No
2) It is standard on all H3s
3) Dallas here -- hit 101 yesterday, H3 cools down quick. No problems with over-heating (at least in my own truck, and no customer complaints)
4) Havent taken to higher elevations personally, but there's been numerous rocky mountain trips forum members have taken and there has been no problem.
5) Can they? Some can -- most wont. And only the best have Hummer Loaners
6) Hummer Roadside assistance comes with the factory 4 year/50,000 mile warranty. The number is 866-Hummer6