If you flush the tranny, you might end up making things worse.
Sometimes the new fluid does a good job and cleans some old
stuck junk out and then it gets into the valve body and makes
the trans stop working properly.
Happened to my brother, we ended up taking the pan off, dropping
the valve body and cleaning the whole thing out, worked like a
champ after, but required several days to get the thin paper gasket
that broke when we separated the plate form the casting.
I use Lucas ATF treatment too, never had a problem with the
trans, even behind the turbo engine, and I have 275,000 miles
on it, never been out of the truck
Wild
Wild