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temperamental shifting

  1. 2002 Temperamental Allison

    01-04.5 LB7 Duramax Powertrain
    Bought 2002 HD truck 3 weeks ago, had it checked out at dealership before I bought it. The problem is when it shifts to 2nd or 3rd or 4th range when driving it normal, occasionally the engine does a brief rev-up during the shift. The shift is not sluggish. I believe it is mainly 3rd gear it does...