1999 Chevy Silverado overdrive shift

1999 CHEVROLET SILVERADO
182,000 MILES • V8 • 4WD • AUTOMATIC
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SKINSFAN69
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I have a 99 silverado 4x4. I just put in a tranny with 35k on it. When I drive it shifts in and out of overdrive. any ideas
Mar 17, 2010 at 10:34 PM
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BLUELIGHTNIN6
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Hello and thanks for donating


You sure it's shifting gears? And not just locking and unlocking the torque converter clutch?
Try it with OD shut off and at a low speed i.e. 35 to 40 MPH. May need to adjust the TPS
Mar 19, 2010 at 12:19 PM
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SKINSFAN69
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I drove it at 65 took it out of o/d rpm went up then i went back into o/d rpm went down it was smooth. There are no tranny codes just a bank 1 air injection code maybe thats why at a sustained speed of 45 there is a hesistation no check engine light on
Mar 19, 2010 at 8:38 PM
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BLUELIGHTNIN6
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what speed is it hunting overdrive at then? other than the OD issue, does it shift fine?
Mar 22, 2010 at 1:01 PM
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SKINSFAN69
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It shifts fine even o/d I think I have a EGR valve that is hanging up or something related to the air injection.
Mar 22, 2010 at 10:00 PM
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BLUELIGHTNIN6
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could try removing the EGR valve and cleaning it along with the valve's passageway. a faulty EGR valve can effect shifting and if you have the MIL on with the code it's def. worth a shot and free to do.
Mar 22, 2010 at 10:10 PM
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SKINSFAN69
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No check engine light on just a guess
Mar 22, 2010 at 10:14 PM