1999 GMC Sierra Hard Shift

1999 GMC SIERRA
199,060 MILES • V8 • 4WD • AUTOMATIC
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USMARINECORPS08
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I drove my truck for about 2 hours at 60-65mph then came to a stop and when I was accelerating it shifted really hard into second. The following shifts were hard but not as severe. I got home and checked the trans fluid. Its clean and full. I was wondering what could cause that hard shift?
Apr 5, 2010 at 3:42 PM
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AMRAAM35
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i had a similar problem with my truck. The seals were worn in my valve body. This caused hard shifts. I purchased a valve kit for about 50 bucks and replaced all the seals and it solved the problem. If you catch it early, you can prevent tranmission damage.

Also check if you have the towing package. When there is this option, you have a tow button on your gear shift that when selected, causes the transmission to shift hard and fast, so it does not overheat when towing a load.
Apr 6, 2010 at 12:24 PM