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Can anyone share some insights with getting the dealer to do the transmission flush on the 8 spd? I can't recreate the issue on demand but it tends to have really hard shifts when its cold, coming out of stop and go traffic, and going up hill. This morning I thought my rear end was going to fall out at the top of the hill but it hasn't done it for weeks. Just looking to avoid the "we can't detect anything wrong" problem. 

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My 18 silverado has been at the dealership for the last week.  They are very aware of the problems with the 8-speed, just describe to them what you posted here and they will more than likely start the troubleshooting by completing the fluid flush.   


The flush worked for mine for about 500 miles before it started up again. Be ready to fight to have the valve body and torque converter replaced. 

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Just take it to them and let them diagnose. They test drove mine and observed hard shifts.   They commanded the trans to do certain things and still had harsh shifts. 


They looked at the valve body and saw it was damaged.   Replaced it and btopped off my trans fluid with the new stuff,  about 8qrts or so.   Not a full flush, jist what was lost from replacing the valve body i assume. 


Its been about 1500ish miles now still shifting pretty darn good n smooth i am very happy and enjoy driving my truck again. 

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