Best transmission for towing?

[Qwazert]

As I mentioned in another thread....I am looking at the 8.1 Vortec because it comes stock with the Allison tranny. Having driven a vehicle with an Allison, I have developed a real attachment to that gearbox...

But the 8.1's seem to be a difficult find around here so I'm starting to wonder if there is another transmission out there that is as capable AND as stout as the Allie...the 4L680 seems to get a lot of praise, but it doesn't have the 6 gears that the Allison does, and with the number of hills and grades I have to tow...a 6-speed is almost a necessity.

 

 

[kstruckcountry]

The newer (2007+) 3/4 ton + trucks will have a 6-speed. It's no Allison but it seems to be pretty robust.

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[Formulabruce]

 the 6L90E

[Super 8]

8.1L and the 4L85E tranny that came in the 2500 avalanche and 2500 suburbans, is also a great combo.

[Qwazert]

Check this out...

https://abbotsford.craigslist.ca/cto/d/2003-gmc-3500-flat-deck-dual/6744533928.html

 

Now I always thought the Allison was a 6-speed (or 5 depnding on the year)...yet when you look at the instrument panel, all I see is PRND321.

My Duramax has the 6-speed and the panel says PRNDM1 and when I place it in M, I see 6 5 4 3 2 1

[redwngr]

 

Kinda side tracking the OP question, but number of available ally ratios depends on the year.

 

 

IIRC they ally became a 6 speed in 2007.5 MY.

 

For sure, the first 5 ratios are exactly the same in the 5 speed and 6 speed versions.

6th gear uses a different combination of clutch packs, but no new gears in trans.

Suncoast (I think it was) offered an aftermarket valve body for the 5 speed that would put the 6th gear clutch combination into service. (so there will be some trucks out there from the 5 speed generation that have been converted to 6 speeds)

 

Other changes in gear and clutch capacity (as well as cooling capacity) were made in the Ally's over the years as the factory output ratings of the dmax improved with each new release.

 

Prior to 2011/LML generation it was fairly common to hear about ally temp concerns (not sure if it was really a problem, but it generated lots of talk and sales of the ally higher capacity oilpan, etc). For -2011+ versions temp concerns are almost never posted in the duramax forums. 

 

 

[john61ct]

8.1L and the 4L85E tranny that came in the 2500 avalanche and 2500 suburbans, is also a great combo.

Exactly what I want in a Suburban for towing, but the 2500 isn't rated for the 12K# I need.

Is it hard / pricy to beef up rear suspension to 3500 ?

[Super 8]

20 hours ago, john61ct said:

Exactly what I want in a Suburban for towing, but the 2500 isn't rated for the 12K# I need.

Is it hard / pricy to beef up rear suspension to 3500 ?

[Super 8]

Above info is in the manual out of a 2005 8.1L 4 wheel drive 2500 LT suburban with factory towing package

[john61ct]

Yes, exactly, that's the data I've been working off.

I will need some loading in the TV as well, and prefer to not go past 70-80% of max rating.

I was thinking I just can't go with Suburban, but they're so much cheaper than the alternatives.

So my question still stands.