I had a "vibration" issue a month ago that was happening between 4th and 5th around the TC. It was more an annoyance than anything. I took it into Lexus Cool Springs and they called and said I needed a new transmission and they don't work on them there so they'd just put a new one it for $4,500. I did some research online and found other GX, LX, T4Rs with same issue and it was solved by flushing old trans fluid out and replacing with new.
I told them to flush it and he got all "well I can't guarantee so you should just replace it". I flushed and it's been fine (even better shifting) ever since.
I'm now a full believer that when they say transmissions have lifetime fluid they mean the "life of the warranty" not your life.
I'll be changing it every 60k now probably. I would have it changed before you do anything. It's not a power flush. They just use a machine that hooks up to trans cooler and runs all the old fluid out replacing with new.
128k on mine
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