First truck ... the truck computer says I'm getting 8.4 mpg?

Just purchased a 2000 dodge 2500 with a 360 v8, 265x75x16 tires, quad cab, 8' bed, I was thinking about the diesel but since it would be used just one in a while, I went the gas engine route.
I expected around 16mpg highway with the 4.10 rear doing about 55, but the truck's computer is saying I'm getting 8.4 mpg with an unloaded bed? I went out on the highway and cruised about 55 for 10 miles and still reading a tenth better at 8.5 mpg. When I fill up I will hand calculate... but how accurate is it to read the mileage from the on board computer?
Is there any sensor or other issue that could justify such a bad gas mileage if I find out that it really is that bad?
Thanks in advance.
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Don't expect16mpg, but 14 maybe with that rear. But 8.5 is more like a v10 mpg, dunno.
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On Wed, 12 Mar 2008 17:06:58 -0700, 0server0 wrote:

May be a little low but I think the 14 is even a stretch for that combination. I would expect 11~12 real world. My old v10 actually averaged the same as what my friends with the 5.2 and 5.9 was claiming around town. I got 10 mpg 12 on a good day when i talked real sweet to it. Most my friends around here were claiming 11 to 13 and I think most of them were running 3.73 or 3.55 gears not the 4.10 you have.
--
Chris

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snipped-for-privacy@comcast.net wrote:

On my 2001 QC 1500 with 360 and 3.55 rear I averaged 14 city, 16 highway.
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wrote:

The 4.10 rear end drops the MPG significantly at higher speeds. On my truck it went from 3.55 to 3.73 and it dropped by 5 MPG at 70 MPH.
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My computer is consistently off by +10% (that is it shows I'm getting about 10% better than my actual mileage). The same goes for the Distance To Empty (DTE). FWIW, my '99 Ram, quadcab, 4x4, 360, 3.55 gears gets about 13-14 mixed highway/city.

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On Mar 12, 8:06 pm, snipped-for-privacy@comcast.net wrote:

'02 Dakota 5.9L: 12 MPG. Sold it!
8.5 is very bad, but I'm not surprised. Depending on the miles, it could be time for plugs, wires, cap, rotor, O2 sensor. Check the air filter.
Also watch the oil consumption. 2 out of the 3 Dodge 360's I've been acquainted with would use up all the engine oil between changes.
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On Wed, 12 Mar 2008 17:06:58 -0700 (PDT), snipped-for-privacy@comcast.net wrote:

Take a cruise down the interstate and check your odometer against the mile markers.
beekeep
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I got 16-17 mpg with my '96 360. It had a 5 speed and a 3.55 axle. Steve
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Broke the crank at first main on my 5.2. Droped in a 5.9 from a 2001. Wacked off a chunk of the flywheel opposite the bob weight on the original flexplate with my end mill. The 5.9 is externally balanced and the 5.2 is internally balanced. Used the 5.2 standard ECM and used the original injectors from the 5.9 by modifying the wiring harness. Worked perfectly and increased fuel economy by almost 2 mpg. As a side benefit, the truck really woke up. Goes like hell. Steve
wrote:

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Absolutely no problem. The truck drives better because the engine produces 40 ft lbs more torque right off idle speeds over the 5.2. So, less throttle is used to get the truck to move and maneuver in traffic. That's where the mileage increase has come from. The difference in drivability is really phenomenal. Dodge really missed the mark when they only offered the combination in the 2500 & 3500. There has been more than 50K miles since this conversion was done. Steve
wrote:

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