Join Date: Sep 2006
Location: Jarrettsville, MD
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The 35s don't help you at all and unless the speedometer has been recalibrated for them, you are driving some miles that are not registering. This could be more than a 10% difference. Still that would only give you 11 mpg.
What type of driving do you do? Idle time is very hard on fuel economy with a 6.0. If you don't believe me just fill up your tank, drive about 20 miles then let it sit and idle for 5 minutes and watch the mpg drop like a rock on the dash meter. Even after you have burned 1/2 tank of fuel this experiment will work. Every 5 minutes my truck idles seems to drop the mpg by .1 or more. Another thing that greatly affects mpg is tire inflation. It gives a more harsh ride but max inflation will yield better mpg.
Exhaust didn't yield me any additional mpg. A zoodad mod didn't give me anything either. My biggest gains have been with SCT custom tuning and a good cetane boosting fuel additive. Tire pressure is another area where I see gains or losses. The air filter is an often overlooked area. I changed my first filter at 30,000 miles and although it appeared to still be clean and the filter minder never moved, It was amazing how much of a change I saw when I put in a new filter. The level of black smoke produced by my race tune tapered off drastically telling me that it was indeed time for a change. Fuel filters also play a role in this equation.