2000 Chevy Silverado .....Tranny problem

I have a 2000 Chevy Silverado, v-6, 171,000 miles, automatic. Tranny works fine for about 20 minutes and then starts to shift really fast
and hard. When I shut it off for a minute or two, it works as if nothing happened.
Any ideas on what the problem may be?
Thanks,
Hank
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I saw a service bulletin that it could be a worn contol valve body.
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I have a 2000(4L60E trans) with the 5.3l and dealt with a similar issue. First, scan the ECM and look for code P1870. On my truck, this code was set but the check engine light never came on. That code tells you that you might have a worn valve body. If you catch it soon enough there are various options including replacing the valve body with another GM part or getting it sleeved. I believe sonnax makes a sleeve for the 4L60E. The symptoms of mine were a hard 1-2 shift when the trans was hot and I got the trans sleeved and a new valve body installed. 10k miles later, no problems.
HTH, Derek.
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my truck,

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when

Thanks for your reply guys.
I am totally confused about this. I do get a harsh 1-2 shift after driving it for about 20+ miles. But if I stop and shut off the igniton and then immediately start it back up and go, it will run fine for a while more. It didn't ahv etime to cool down if heat was the problem or any other mechanical problem. Could it be from some electrical problem?
Thanks,
Hank
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Hi,
At wits end here as the better half (ha) pulled my starter, bought me a book and a new starter and says install it. OK, so now the new starter is now installed however still whenever i attempt to crank it, i hear what sounds like fuel dispenser engaging but nothing else (not starting). Now...battery checks out good and shift ok. Open please for more troubleshooting areas as i'm not getting much else from two books.
TIA!
Desperate mum in Alabama
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Fuel dispenser?
Is the engine turning? Can you feel it turn? If it has a distributor, can you see the rotor turn?
If the starter doesn't engage into the flywheel, it will just turn itself and not turn the engine. The sound will be different than normal, but you'll hear the starter. --scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

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ook

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Quit changing the subject heading.
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