I have a 1993 K1500. I had the transmission rebuilt in 2007. Shortly after the rebuild. It started changing gears really hard from 1st to 2nd when it is first cranked up. After you drive it for about 10 mins. It changes smoothly until you cut the truck off, and let it sit for awhile. Then it changes hard again for about 10 mins the next time you crank it up. The place that rebuilt it says it is not the transmission, but could be a mapping sensor controling the idle speed.
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