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Any feedback on the 496 gas motors w/ the Allison 5 speed automatic? Looking at one today - it's a 2001.....

any thoughts?
 

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4-8 mpg city 11-12 mpg highway
 

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We've got two of them and I'm not impressed. Seems like you work them to death with any kind of load on and the mileage sucks.
 

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4-8 mpg city 11-12 mpg highway
There not that bad, thirsty but not 4mpg!!!
I love mine, even put the ol girl away in winter to make it last.
Cant get a new one with a 8.1!
 

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I here back from customer that they get between 4-8 mpg city depending on a whole host of things.

There not that bad, thirsty but not 4mpg!!!
I love mine, even put the ol girl away in winter to make it last.
Cant get a new one with a 8.1!
 

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I have a 2001 Suburban with the 8.1/4L80e and absolutely LOVE it.

It tows like a fucking animal.

The first thing I did was swap-in a new PCM from Nelson Performance. When I first got the truck, I thought it should run a little better. They are seriously detuned from the factory. (feels like a big smallblock)
After the new PCM went in, it was a whole 'nuther animal.

Best mpg I've seen and documented was 13.99 on a trip from OC MD to Reading, PA... fully loaded with wife/kids/luggage.

In a heavy 2500HD, I wouldn't want any other motor.

FWIW, the FP regulator can be tweaked a little for better mileage/performance. 58-62psi is where they like to run. 58psi is where I have mine right now. At 62psi it ran better but guzzled alot more gas.

 

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I bought a 2001 Chevy 3500 Dually with the 8.1 and Allison. It was a 4-wheel drive extended cab. Driving as a daily driver I got 9 mpg if I ran it real hard and 11 if I took it easy. That was a combination of city and secondary roads. It didn't do much better on the hiway. Towing a heavy 28 ft trailer with car, cart, tools and four people it would get about 6-7 mpg depending on the hills. I traded it in on an 04 with the Duramax. It had about 70k when I traded it and I never had it back to the dealer for any repairs.
 

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The 2001-2003 8.1's are notorious for massive oil consumption.My 2002 2500HD drank a qt every 800 miles or so and got 10mpg empty and 5-7 pulled a 10,000 lb 28' tag trailer.

I wouldnt own another that's for sure with 4.25 a gallon gas.
 

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My bosses gets about 8-9 mpg around town. There is a TSB on the oil consumption, new intake bolts and a new revised torque amount. Went from a quart a oil every 1000 miles to about a quart of oil every 3000 miles using 5w-30 Amsoil synthetic oil. I myself am a diesel man. My 02 2500HD Duramax gets 17 mpg around town. Last time checked diesel wasn't twice as much as regular so you do the math.
 

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My 01 has 175,000 miles on it and the only problem i've had is a crank trigger sensor went out at about 100'000.Get's 11mpg no matter how it's driven and get's 8 pulling a 28' enclosed trailer fully loaded.
I love the allison tranny too.Does take a little getting used to though.As far as oil consumption it uses a qt. about every 3,000.
 

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My bosses gets about 8-9 mpg around town. There is a TSB on the oil consumption, new intake bolts and a new revised torque amount. Went from a quart a oil every 1000 miles to about a quart of oil every 3000 miles using 5w-30 Amsoil synthetic oil. I myself am a diesel man. My 02 2500HD Duramax gets 17 mpg around town. Last time checked diesel wasn't twice as much as regular so you do the math.
dont trade your 02 duramax for a 08 duramax, mines lucky to get 15 on the highway, and 7-8 pulling a gooseneck enclosed
 
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