The failure rate of commercial Humvee's is incredible. They are not built anywhere near to the standards that the military ones are. And most military people will tell you the military version also has a penchant for breaking down as well. A company I worked for bought one for promotional uses and to drive the winners of a contest to the Sugarbowl and that thing was in the shop EVERY week. Needless to to say the company flew the winners into the bowl game instead of risking humiliation when the vehicle broke down on the way. That vehicle sits on a lot now collecting dust as a big unmovable banner now withe companies logo on it.
Get a real military Humvee if you need that level of offroading ability, or you could just do what everyone has been doing around the world for the past 20 years and get a standard 4-wheel drive vehicle. Humvee's are serious overkill and not worth the effort it takes to maintain them.
JD Powers rated the Hummer a 5 out of 10 for reliability. Not great for what you pay for them. Almost all models rate this way on reliability. Performance is high, but what good is performance if you can't get it to run?