Just wondering if someone can gimme an idea of what mileage I should expect.. I have a 99 C1500, extended cab, auto, 5.7 Vortec with 118K total on it, all 100% original except for the tires, have gone to a 31-10.50-15.............recently I have done a complete tune up, cap, rotor, wires and plugs, along with pcv and fuel filter......I keep it very well maintained and it runs like a new one (and drives like a new one now with complete front susp rebuild).........One thing I CANNOT seem to find a timing tab...if it is there its where I cant see it........hook a timing gun to it, and the timing mark is dead on straight up on the damper.......if you move the distributor more than just a little bit, the "service engine soon" light comes on.........retard or advance, move it back and the light goes off............anyway, like I said, it runs great and the plugs look good, I average about 15-15.5 mpg on regular unleaded with kind of a mixed driving, highway/city.....it does show to have a rearend code of GU6, which I think should be a 3.42 ratio.............any thoughts on this mileage, or ideas on the timing tab ?