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Silverado engine or tranny problem?

Discussion in 'GM Powertrain' started by Silver1, Sep 13, 2009.

  1. Silver1

    Silver1 New Member

    Hey guys,

    New to the site, I have been having a problem with my 1999 Silverado 4x4 4.8L , Everything works fine, tranny shifts with no problems, but it seems when im driving between 40-55 mph (70-90kph) and im depressing the accelerator slowly right before it wants to shift into overdrive the truck studders or jerks alot, almost feels like a tranny slip, but my idle doesent change, could it be a bad misfire? is there an overdrive sensor of some sort? Fuel problem? , more so happens up hill. Its hard to explain, Engine idle at the time is around 1000-1500 rpm, just before downshift into overdrive. but doesent happen all the time. any info would be appreciated. Thanks
  2. Jimmiee

    Jimmiee New Member 1000 Posts

    It's probably a misfire. Drive it until it misfires and then lightly depress the brake with your left foot while maintaining the condition with your right foot. The misfire should go away when you do this. Also if you get your truck scanned you will probably see a freeze fram pending code for the misfire.
  3. Silver1

    Silver1 New Member

    I will give that a shot and let you know how it goes. thanks for the help
  4. jtwh20

    jtwh20 New Member

    Change your sparkplugs - check wires and cap - I had the EXACT issue on my 95 burb - I swore the tranny was failing - installed new plugs and it shifts / runs like new - 198k :)

    ALSO make sure the plug gaps are correct - the ones i removed were waaay off .45 too large
    Last edited: Sep 13, 2009
  5. Silver1

    Silver1 New Member

    Thanks. do you recommend Ac Delco?
  6. jtwh20

    jtwh20 New Member

    I just went with Autolite - I couldn't find 8 AC delcos in a hurry
  7. Silver1

    Silver1 New Member

    I tried this and when i did it, it dropped to overdrive fine is this good? or a sign of something?

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