I just purchased a 2004 3500 srw,4x4 auto, 21,000 miles. I don't believe it has done very much towing. I am getting 11. 5 to 12 mpg on the highway at 60 mph. I installed a new air filter, fuel filter, and it has 35" tires. I just sold my 99 Dodge 2500 4x4 5 sp, 193,000 miles and almost always...