You want to know the truth? They probably either did exactly what you told them not to do (a full flush), or they did a drain and fill and charged you for too much fluid. The thing that probably wasn’t good for your car was letting it go 138,000 miles without doing maintenance to your transmission.So is what they did not good for my car? I always hear things about how flushing it when you never serviced it before can actually damage it?
Is it all possible that they did two drain and refills? I specifically told them not to do a flush, and the invoice says they performed a drain and refill so I guess I have no clue what was actually done. Maybe they overcharged me on the fluid?
And is the flush not good for your car? I’d say by the sounds of it, it actually helped (as your torque converter shudder went away). I wouldn’t worry all that much about a “flush”, it’s just an exchange of fluid.
Best advice, keep an eye on it now, because if that shudder comes back you want to take full advantage of that extended warranty.