Is 3.42 gears and p265/70r17 tires a good combo with 5.3 chevy silverado 4/4 I'm...

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...wondering about gas milage I'm thinking about buying this thruck my drive to work is 100 miles round trip. I don't tow any thing very much so I know the 5.3 may be over kill but the dealership is offering a good deal on it. I have a small family so the roomy interior is a huge plus to me