I have found several nice Avalanche with the 8.1 but how do i knowif it has the Allison Transmission? Seem to be quite a few more Avalanche on the market with 8.1's than just he standard Chevy/GMC 2500 wonder why that is?

Avalanche 8.1 will have a 4L80E...still a good trans

I'll give you $1500 AND I'll toss in my Dodge Ram 2500 for FREE. See you tomorrow. Have it washed.

One i found the service manager said 4L85E what does that mean any idea?

nothing wrong with the tbi's ..you just have to know what to do with them,,for one they retard the crap out of the timing..everyone i have worked on was 2* retarded.timing..next order a piggy back chip that plugs into your pcm,,next,,get a adjustable fuel pressure regulator and crank up the fuel pressure to 16 psi @ wot..gm has them set at 13 psi and they lean out when you stick it to the floor,next install a msd 6al2 box..mine rips still and it has 470,00 k on it...i get 10 around town and 14 pulling my 4 place enclosed low profile trailer on the hyw,,but i have to keep it unser 70..its a suburbas with 3.73 posi and 285/75/16 tires..ps i put the timing @ 4*..

clean 2500 HD 6.0 w/ under 100k miles for 8-12k. If the tranny bothers you... you can rebuild a 4l80e for 1500 bucks if you r/r yourself not to mention it is a very good tranny anyway

i really feel that the front of the frames on gmt400 trucks is too weak for a solid axle (over time it will crack), i would rather start with a clean k30 frame

4L85E is AKA the M32. Not a big deal. ALL of the 2500 Suburbans and Avalanches came with this transmission when mated with the 8.1L.
It's a 4-speed with Overdrive.

It's not the Allison 5 speed automatic, but it does fine.

I had a 2500 Avalanche back in the day, and posted a bunch of info here on OSO in the past.
The 4 Speed Automatic can't handle the torque the way the Allison can, so on the 2500 AV/Suburban it is electronically limited to reduce the torque by 30% until you get out of first gear (from a dead stop). You can use an aftermarket tuner (I like the Diablo Sport Predator) to get that torque back, but you do have to go easy on the go pedal. The 8.1L has a LOT of torque, and with a few mods it makes even more.

For the above reason, IF you can find a 8.1L in the 2500 Truck platform, it will have the Allison 5 speed auto, or the ZF 6 speed manual--AND you will have a bit better setup, but there is nothing wrong with the 4L85E in the Avalanche/Suburban 2500.

The vortec version is better than the tbi. They are 9:1 vs the tbi 7.9:1, roller camshaft, better heads, port injection runs much smoother and cleaner,obd ii pcm, the engine doesn't run out of steam at 3500rpm. Stock they have torque management like the 8.1 . I had mine tuned and torque management removed. With the tune it is quite a bit peppier.

Stock injectors are known to leak along with the fuel psi regulator. Replaced my stock injectors with LS6 injectors out of a 02 vette. Needs to be tuned for these since they are larger. But stock ls1 injectors from a 98-00 ls1 can work without a tune.

I forget the specifics of the 4l80E but sometime in the 96-98 timeframe, they made some internal improvements. My dually has the 14 bolt GM rear axle.

As for the solid axle swap, I have no input. I am fine with the stock torsion bar independent front suspension. I only use 4x4 at the ramp. I actually think the truck rides pretty decent for 4x4 dually .

Yes that transmission is fine. It is the same family as the 4L80 , The 4L80 and 85 are based off the old GMT 400 which was a bulletproof tranny from the 60's and added an Overdrive gear and lockup. I have 135k on mine with no major issues.

You should get 11-12 mpg in town and 8-9 towing. If you get the Avalanche 8.1 I would tune it with a Hypertech tuner- it did wonders for mine- added another 500 rpm usuable range. Also gave me about 0.5 mpg

Wannabe