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  1. #1

    Default HARD shift after driving for 30 minutes


    I have a 99 GMC Suburban LS 4x4, auto trans. I just bought this truck and previuos owner had it sitting for 5 months. I have put 500 miles on the truck.

    It shifts smooth as silk when running 20 minutes or less. If I run it longer, I get very HARD shift on 1st and a medium HARD shift on 2nd. Truck has 173k miles.

    Trans fluid looks good and does not have a burned smell.

    What steps should I take to resolve. Do the Trans coolers go bad and need to be replaced? Do I need to get a trans flush ? Do I ndeed a repair?

    Any help would be apprecaited.


  2. #2
    Join Date
    Feb 2011
    Locust Grove, Georgia, United States


    your valves in the valve body are getting hot and sticking
    1999 GMC Serria
    Regular cab short bed
    4.8 Vortec (6.0 swap soon)
    Custom cold air intake and spacer
    Bullydog GT programmer
    Flowmasters with turndowns
    55w 12000k Hids highs and lows with low and high relay
    Viper Remote start
    L.E.D.s Everywhere
    200 psi Train horns and onboard air
    16X8 HELOS
    285 Courser M/ts

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