I have been living with a crunchy 4-3 downshift for over almost 2 years now.
I replaced the shifter bushings and it made no difference.
I tried the 50/50 ATF flush and it helped a little but mostly I have just avoided that downshift, double clutching hasn't helped much either.
Then last month it started to crunch on the upshift.
I went looking for and found another trans to swap out, but was in the hardware store the other day and saw a product I haven't seen in years.
MolySlip "G". (Moly additive for gear oil.)
We used to use it years ago with amazing results but haven't been able to find it in a long time.
At >$20 I figured it couldn't hurt.
Just put 200km on it with the goo in, no more crunching on the upshift, the dowshift feels a bit notchy, sometimes, but no CRUNCH, and seems to be improving with driving.
Feels like the 90% solution, at least for now.
Might be worth a try, for those that are having issues.