I sold my my 06, manuel transmission quad cab (Boy am I kicking myself in the **** - looking back I would have never sold it!) It had 55,000 miles

Bought an '05 automatic with 40,000 miles.

I swear in my '06 I was getting 15 - 17mpg and on the freeway I could get close to 18 or 19.

The day I bought my '05 I filled it up and reset all the panels and the overhead has been reading 11mpg. I had only gone through 1/4 tank but I couldn't stand it so last night I went to the gas station and filled up to check it. Sure enough 11mpg!! ***? I have not been driving any different than my '06

I reset all the panels and I'm testing the mpg again. I have been trying to drive very much like a grandpa (rpm's not over 1500!!) - everyone is passing me like crazy but my panel is now reading 15 mpg. Again, I'm driving way more conservative than I did in my '06.

What do you think. Only modifications on the '05 is the new lift, 35" tires and wheels. The '06 I had the edge chip on stage 3 90% of the time and it was a 6 speed.

 

In my experience the 6sp gets better mileage. Does your auto have 4.10s or 3.73s?

 

Good question. I don't know. How can I find out?

 

I would say the Edge and the fact that the 06 was a 6 speed, probably made a big difference in mileage between the two. The 6 speed is geared kind of low as it is, so adding those taller 35" tires probably got the engine right into a nice mileage power band.

I would wager to bet that the 05 has 3.73's in the rear end. You can find out by looking on a sticker that could either be under the hood, on the side of the drivers door, or in the glove box. I can't remember off hand exactly wear they list them these days. What are your RPM's at say 60 or 70? At 70 w/ 3.73 and stock tires you should be turning about 1900 rpm. So at 70 with 35's I would figure your down around 16 - 1700. If that's the case, your probably just working the engine to much with those tall tires and a high gear ratio. The engine never really gets a chance to relax.

 

Isn't the Ultra LSD in more and more places now? they say that hurts MPG by nearly 2. i wasnt paying attention this spring to which i was getting, but im thinking it was the ultra low because my milage sucked coming out of winter. so i dunno seems better now. and ive been making sure to get LSD if possible.

 

Have you adjusted your speedometer yet for the bigger tires? If your running 35's that puts you a little over 10% off on your speed and mpg figures, so you need to add that back in.

With out re-gearing that puts you at an effective gear ratio of 3.37:1 and at about 1,750rpm's @ 70mph or 1,500rpms @ 60mph. At HWY speeds your about 200rpm's lower than stock 3.73 Auto trucks. That's somewhat good for HWY flat cruising @ 65-70mph... But not so good for slower city speeds and towing as your engine will be lugging more below 1,500rpm's or will have to shift out of overdrive into 3rd.

Your stick was simply geared lower from the get go in stock form, so adding 35's to it kind of balanced it out to what you'd expect from a stock auto.

I've gotten 22.7 mpg per my OH w/92%HWY/8%City....that comes out to about 20.6 mpg hand calculated!