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  1. #1

    Default Torque converter lockup, 05 yukon xl

    I am curious how I can tell if my converter is locking up on the freeway. My freeway mpg has recently decreased to less than my city mpg. I think that I can feel it locking (which I know is not normal) When I get on the freeway, accelerate slowly to 68mph, I feel an "extra shift" or bump at about 50-55mph. ( I really have to concentrate to notice it) I am just wondering if it is not locking and destroying my mpg. The truck runs great on the freeway, just decreased mpg.

    1995 Silverado 4x4
    6" BDS Suspension Lift-3" Body Lift-Add A Leaf in rear -Trailmaster SSV Shocks-Duel Steering Stabilizer Kit -AirAid Cold air intake-
    4.56 Gears with Detroit Auburn Locker-Pro-Comp Traction Bars with duel shocks-Aluminum Skid Plate Kit-38.5" x 16.5" Mickey Thompson Baja Claws-Constant Dropping fuel gauge

    2005 Yukon XL Jet Power Programmer, Bilstein Shocks, Bilstein rear springs, Helwig Anti-sway bars, EGR Window Visors, EGR Hood Shield, Denali Headlights, Headlight harness upgrade, GE NightHawk Bulbs, White Night Rear lighting system, Russell Braided SS brake lines, PowerStop Brake pads, PowerStop cross drilled and Slotted Rotors,
    2002 Silverado ext cab 2wd (Sold)
    2003 Yukon XL (Totaled)

  2. #2
    TRPLXL2's Avatar
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    Jan 2009
    Norwalk, Ohio
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    If you have a scanner that can read transmission data that's how I do it, I leave the scanner plugged in and drive and watch the t/c lockup status. It will say open or closed.
    2004 Chevy Colorado
    LS1 5.7 swap/TBSS rear axle swap

  3. #3


    Sorry Mike, I missed this earlier. You should be able to tell watching the tach. If the tach rpms change very little when you push the pedal around 65, the TC is locked (and engine rpm is tied to rear axle/wheel speed). If the engine speeds up easily, the TC is not locked.

    '09 Avalanche LTZ - Black
    '05 Envoy XL (sold)

  4. #4


    If you accelerate slowly, you can feel the lockup, and that is normal. The reason your mileage has dropped is due to the oxygenation of fuel in your area, which generally begins around Nov. 1, and ends around May 1. It will cost you 1-2 MPG, and there is not a thing you can do about it, except to thank your liberal environmentalist politicians who know virtually nothing about vehicles.
    Las Vegas, NV...2001 Silverado 1500 LT Z71 Stepside X-cab, 171,000 miles, 5.3, cat-back duals, leveling kit, 3.73, 17" rims, more to come...

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