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Thread: 5 to 6 speed conversion

  1. #11
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    Quote Originally Posted by THEFERMANATOR View Post
    If you have an 8.1L though, you CAN swap in a GEN IV TCM into it and 6 speed trans and wiring and have a 6 speed as the SUNCOAST kit doesn't work for gassers but the GEN IV 8.1L TCM does talk in low speed J1939 can like teh older 01-05 trucks used(all of the 8.1L's used low speed data).
    I have a early 2004 8.1L/Allison (1000PK) the numbers on my TCM are PN 29537441 11/19/2003 S/N: BKDUTCM333230962 Brodcast Code 9833 230962 Service Number 15768288

    I am sure that tells you anything, but I was wondering just what exactly I need to convert over to the 6 speed. I do a lot of driving and squeezing more MPG out of my truck would be very helpful.

    Thanks
    Ryan

  2. #12
    Lifetime Member THEFERMANATOR's Avatar
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    Theres a few write ups on it, but the 06 8.1L TCM uses the old style data communications. So you can swap to an 06-07 trans, wiring harness, and TCM into your older 8.1L and make it work. In the end the milage savings will probably never equal out what it woul cost you to swap everything over. There has been a few that have done it in the past, but the cost was a factor.
    1995 GMC 2500 SUBURBAN powered by 01 DURAMAX/ALLISON, little of this, a little of that,
    DIAMONDEYE 4" exhaust, CORSA muffler, AFE stage 1 dry filter, custom tuning by me, KENNEDY single pump and pump rub kit.

  3. #13
    Member Whipped383's Avatar
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    Im in the 8.1 boat as well. I just saw killerbee listing tcms on ebay and was wondering if anyone had more info on this. Is there a reason the suncoast kit wont work on the gassers? And links or writeups on doing the 6 speed swap on a gasser?
    97 K1500, 383, 4L60E, Whipple, Stock 14 Bolt with 3.73, EFILive V2, 0411, Marine, #42 Injectors, H-Boost, LC-1, Coming Soon: Intercooler, Trutrac, 4.11 gears?
    03 K2500HD, 8.1 and Allison, Stainless works long tubes, Intake mods

  4. #14
    Lifetime Member Cougar281's Avatar
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    Default Re: 5 to 6 speed conversion

    The suncoast kits are designed for the duramax. The valve body would work, but the tcm would be all wrong. They MIGHT be able to make a TCM for a gasser, but personally, I wouldn't touch one of their 6 speed conversion tcms with a 10 foot pole.

    If you have a 03+, are mechanically and a little electronically savvy and have some patience, you could probably get a 6 speed transmission, body harness and TCM for less than their TCM. IIRC, I paid less than 1k for my 6speed trans and was able to more than recoup that when I sold my freshly rebuilt 5 speed.

    If you have a duramax, IMO, the ONLY way to do it is to completely convert to a lbz/ 6 speed as I did. If you have an 03+, its largely plug and play. 01-02 not so much. That way you get all the 6speed benefits (including tap shift and the enhanced winter warmup idle which works much better than the 04 lly winter warmup idle) and a stock, not butchered TCM.

  5. #15
    Member Whipped383's Avatar
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    Iv got the 03 with an 8.1. So I would need a completly different trans not just a valve body swap?
    97 K1500, 383, 4L60E, Whipple, Stock 14 Bolt with 3.73, EFILive V2, 0411, Marine, #42 Injectors, H-Boost, LC-1, Coming Soon: Intercooler, Trutrac, 4.11 gears?
    03 K2500HD, 8.1 and Allison, Stainless works long tubes, Intake mods

  6. #16
    Lifetime Member Cougar281's Avatar
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    Quote Originally Posted by Whipped383 View Post
    Iv got the 03 with an 8.1. So I would need a completly different trans not just a valve body swap?
    The valvebody would work in the older trans as long as you also replaced the wiring and TCM, but it might be tough to get just a valvebody.

  7. #17
    Member Whipped383's Avatar
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    So whats involved in just modifying the valve body?
    97 K1500, 383, 4L60E, Whipple, Stock 14 Bolt with 3.73, EFILive V2, 0411, Marine, #42 Injectors, H-Boost, LC-1, Coming Soon: Intercooler, Trutrac, 4.11 gears?
    03 K2500HD, 8.1 and Allison, Stainless works long tubes, Intake mods

  8. #18
    Lifetime Member Cougar281's Avatar
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    Not modifying - replacing. You'd have to swap in the 6-speed valve body (and associated solenoids), IMS (NSBU), wiring harness, external wiring harness that goes between the TCM, transmission, fuse box, ECM and I'd assume engine (not sure on the gassers)...

  9. #19
    Member Whipped383's Avatar
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    So what about using the TCM killerbee is selling? Its a modified stock TCM like the suncoast kit. I know someone mentioned the suncoast TCM has to use a modified valve body and not just a 6 speed valve body because the solenoids where different
    97 K1500, 383, 4L60E, Whipple, Stock 14 Bolt with 3.73, EFILive V2, 0411, Marine, #42 Injectors, H-Boost, LC-1, Coming Soon: Intercooler, Trutrac, 4.11 gears?
    03 K2500HD, 8.1 and Allison, Stainless works long tubes, Intake mods

  10. #20
    Lifetime Member minytrker's Avatar
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    I have a 2003 duramax dually and will need a trans in the next year. Is it worth the money to upgrade to the 6 speed?
    99 Z28 Camaro|LS1 Heads & cam Tuned by LSX Power Tuning
    2003 CC Duramax Dually|19.5 w/245/70/19.5|Tuned by LSX Power Tuning|5in exhaust
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    2006 CTS-V K&N CAI|OBX Headers|Cammed LS3|Tuned by LSX Power Tuning|

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