I have a 2016 Chevy Suburban with 99k miles. It doesn’t pull once it warms up.

The transmission shop says there’s no code, so the issue is mechanical. They want to pull the transmission out completely to diagnose it, which would cost $1000.

They also mentioned that the transmission oil is black and has a lot of debris, which settles so the truck pulls when cold but once the oil is warm and starts moving, it loses pull.

I’m wondering if a potential fix could be to just change the transmission oil and see if that helps.

The shop is unwilling to try this approach and wants to open it up. I just want to make sure I’m not being scammed before I give the go-ahead to pull out the tranny.