transmission issues, replacement transmission experiencing erratic RPM spikes and harsh shifting at low speeds?

2020 CHEVROLET SUBURBAN
110,000 MILES • 5.3L • V8 • 4WD • AUTOMATIC
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THEFUTURE
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Original Transmission failed; suburban would not drive at all. had a dealer replace it with a remanufactured one, which I supplied. Within 10 to 20 miles of driving with the new transmission it started acting strange, erratic RPM spikes and harsh shifting at low speeds. took it back to the dealer, they claim it's the valve body, $$$. My original invoice shows only 5 quarts of fluid, i can only assume they did not flush the entire system before installing the new transmission. Otherwise, it would be 11 or so quarts. Question, would this lead to the new transmission acting this way? thanks
Apr 4, 2024 at 4:24 PM
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STRAILER
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If they did not flush the cooler lines and replace the radiator this could be the problem, if the old transmission came apart and spread metal inside the cooler (in radiator) the metal could have traveled into the new transmission. But let's run the codes to see if any codes are stored, this guide can help:

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

You are correct on the fluid volume; it should be about 12 quarts of fluid. Did the dealer give you any codes that they found to determine if the valve body is bad? Here is how to change it out in case this is the problem. Check out the images (below). Please let us know what happens.

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Apr 5, 2024 at 9:53 AM
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THEFUTURE
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no check engine light on, but scan tool reads a p0842 code, transmission fluid pressure switch 1 circuit low voltage.
Apr 5, 2024 at 10:05 AM
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STRAILER
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This can be because of the switch or the low fluid pressure due to a clog. The location of the switch is inside the valve body, this is probably why they said you need a new one.
Apr 5, 2024 at 5:35 PM