lookin into joining th darkside. im currently in the research phase. i want to be able to get good gas milage, and still have a decent amount of power. i would be swapping in a 4L80E most likely at the same time. is the 6.5TD swap that much more hecktic than the 6.2? i like the idea of the 6.5 since there are more performance options out there for it. what would the gas milage difference be between the two? with overdrive 5.13s and 40's what would be some realistic mpg numbers in town/ and in the city?