Mine was awful, when I bought it 12-13 in town & maybe 15 on the highway, after changing the O2's and a couple mods my normal went to 15-16 in town & I have gotten 21 on the highway. After the SC if you drive it sensible, you still get 15-17 in town & I have gotten almost 24 on the highway. The 3.0 spends so much time in the gas sucking mode during even light acceleration its ridiculous, The SC really helped that area, even for fuel mileage. I have a scan gauge and you can watch your instant mpg & attempt to adjust your driving habits accordingly.
All you have to do for the O2 is drill a hole into the header to clear the end of the O2, then weld the bung into the collector area on the header in a location near where the stock O2 is located, any good muffler shop will have the bungs & be able to weld stainless, should not be more that $25- 30 to do it
JP02XLT