Forum Discussion

Brisk's avatar
Brisk
Explorer II
Mar 23, 2015

GM 6.0/4sp vs. 8.1/Allison vs. 6.0/6sp

Hi all.

My Towrig in Sig is getting a little long in the tooth. We just bought a New to us Toyhauler which is quite a bit heavier than our old trailer and my truck is hating life lol!! We were planning on upgrading the truck next year anyway but found a trailer we loved so we did that first.

Old 5th wheel was 8k ready to camp. I haven't weighed the new one yet but dry weight is 8200 so an educated guess would be 9500-10500 without "toys" and 12k with.

My plan is to buy a newer used truck in the next year. I have always had GMs and have had great luck with them and I know how to fix them so my plan is to stay with GM. I DO NOT WANT A DIESEL

I am curious if anyone has first hand experience towing with an 8.1/allison truck or a 6.0/6sp truck compared to a 6.0/4sp. Right now I am pulling 6% grades at 35-40mph in 1st gear (my old trailer was 60mph in 2nd)and running in 3rd at 60 on the flats at about 6.5-7mpg (old trailer was 4th at 60-65 and 8-9mpg) I am wondering how much of an improvement I should expect with an 8.1 or a 6.0/6sp.

I know what the tow ratings and hp/torque numbers are but I am looking for some real world experience.

Thanks in Advance!
Tow Vehicles
  • BurbMan's avatar
    BurbMan
    Explorer II
    Mar 23, 2015
    The Ally was standard with the DMax but I thought it was optional with the 8.1, maybe I'm not remembering that right. I know wasn't available at all in the burbs :(

    The base trans in 01-02 was the 4L80E, then in 2003 the 4L85E. Look for the RPO code sticker in the glovebox when you are shopping, MT1 is the 4L80E, MN8 is the 4L85E, M74 is the Ally.
  • Brisk's avatar
    Brisk
    Explorer II
    Mar 23, 2015
    I am pretty sure the Allison was standard in the 2500hd/3500 8.1 trucks. I know the Suburban and Avalanche had the 4L85E due to fitment issues.

    I need a crew cab srw 4x4. I know they are few and far between but that is why i am starting my search now and am also considering 2007.5 and up 6.0 trucks with the 6sp auto. (Assuming one will pull significantly better than my current truck)
  • BurbMan's avatar
    BurbMan
    Explorer II
    Mar 23, 2015
    The Allison trans was an option with the 8.1L, if you could find one it would certainly do the job for you, but '08 was the last year for those in a pickup. Most folks that tow heavy ordered the DMax, and only a few 8.1L buyers paid the $$ to upgrade to the Allison...so good luck finding one.

    Just did a search and there are only 49 8.1 Chevy or GMC trucks in the whole US on Autotrader, only a few of those will have the Ally trans.

    Here is an GMC extended cab dually 8.1/Ally with only 30k miles about 300 miles from you.

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