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Four years ago I bought a '95 Lexus ES300 that shifted very smoothly
but had dark brown transmission fluid. I had the transmission
power-flushed on a T-Tech machine and immediately thereafter the shifts
became harsh and slightly erratic. Somebody suggested that dirt
dislodged by the flush had probably clogged/damaged the valve body.

Over the next 4 years I drained and filled the transmission a number of
times, and each time shifts would get smoother for a few days. Last
month I finally had it power flushed again, and this time there was a
significant but temporary improvement.

Does this sound like a valve body problem? If so, how hard is it to
replace (with a remanufactured unit)? Is this something that can be
done in a few hours by a non-professional without specialized tools?

Thanks,
Tripurari