Have to agree with SnoMan, I had a '77 Impala with the same tranny, never
made it to 100K miles. Shop told me it was a lightweight transmission and
not durable and replaced it with a rebuilt T350. Drove that for 175K more
miles with zero service. I seem to recall they had to run a vacuum line to
it, as the 200 had a detent cable but the 350 worked on vac, or maybe it was
the other way around.