Just to throw some wrenches in. Not sure if you have thought of these yet or not, but some other SUV/trucks ive seen with good towing ratings.
New Colorado/canyon. small truck but decent MPG and rated at 7000lb towing.
http://www.motortrend.com/oftheyear/...k_of_the_year/
or the Jeep with the Diesel, prob expensive still..
Same with Touareg or Q7 TDI's. 7000k towing and close to 30 mpg.
http://www.motortrend.com/roadtests/...uv_comparison/
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