Poor gas milage for 03 Tahoes - Flex Fuel chage culprit?

A friend of mine has an 03 Tahoe and complains of poor gas mileage. I have an 01 and get better mileage than his. Both are 5.3 liter plants. City mileage: 17 (mine) vs. 14 (his)
Is this because of the "Flex Fuel" change to the engines? Here in Houston there are no "Flex Fuel" stations. So it's kind of an overkill to sell those vehicles here.
Comments?
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oops I missed the figures in your post. Tell your friend he should feel lucky. My last fill up was 10.09 mpg. If I could get his ratings I would be happy. Most all I have compared to get 14-15 city or overall and about 18 on the highway. Don

have
Houston
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Lets do the math... 5000lb vehicle + 5.3L(325 cubic inch) engine + city driving with A/C on poor mileage.

those
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