poor gas mileage

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I fill up when the light comes on and the miles are city and highway. I do not know what gears I have. How can I find that out ?
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There should be a tag on the differential cover that is held on by one or two of the differential cover bolts. It'll probably be 3.73 or 4.10. If there is no tag. you could lift the rear wheels off the ground, put the transmission in neutral and count how many times it take to turn both wheels in order to get the drive shaft to make one complete turn, or a dealer could probably tell you just be running the VIN.
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Ed H. wrote:

Or look at the sticker in the glove box
G72 AXLE REAR, 2.14 RATIO G75 AXLE REAR, 3.62 RATIO G76 AXLE REAR, 3.36 RATIO
G90 AXLE REAR, 3.15 RATIO G91 AXLE REAR, 3.08 RATIO G92 AXLE REAR, 3.08 RATIO, PERFORMANCE G93 AXLE REAR, 3.27 RATIO G94 AXLE REAR, 3.31 RATIO G95 AXLE REAR RATIO, ECONOMY G96 AXLE REAR, 3.55 RATIO G97 AXLE REAR, 2.37 RATIO
GT4 AXLE REAR, 3.73 RATIO
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Look in the glove box for the RPO options tag. It will tell you what gears it has along with most of the options on the truck as well. Then look at http://www.wiu.edu/users/muwtj1/rpocodes.htm or http://www.c2e.info/rpocodes / to find out what they mean.
--
Steve W.
Near Cooperstown, New York
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snipped-for-privacy@yahoo.com wrote:

Me thinks this is your problem, there is no overdrive button. OD is another notch on the shift lever, the button is two/haul mode. If your running around in tow/haul mode that could account for the low mpg.
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My Chevy is a diesel so I can't compare it to your GMC, but comparing it to my Dodge, which runs just below 2000 RPM at 70 MPH, it may be that the overdrive isn't engaging, which could account for the difference. Please note however, the overdrive on my Dodge is pretty tall (IIRC .67:1 gear ratio).

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Overdrive, that is a good point. Can you feel it shift through all the gears into OD?

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2006 1500 Z71 5.3L 3.42 gears Reg Cab around 5k on the odometer
Most of my driving is just puttering around town and I get 15.5 MPG.
Drove it 1100 miles with about 1000 lbs in the back and got 19 on the road.
I buy cheap gas, Wal*Mart, Kroger's, etc.
Karl

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snipped-for-privacy@yahoo.com wrote:

christ, a little info on motor would be nice
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Since you can't tell what gear you are, why don't you redneck it. The stick on the column, put it in 1st, go, then 2nd, go, than 3rd, go, than D, than go some more. You should see something happen on your tach. That will tell you if your tranny still had OD.

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