RLE Trans downshift issue

[JustSumDad]

2005 Libby 3.7L V6 auto RLE transmission question.
Just had a look at a KJ for my daughter, looking at an 05 with a date stamp of 06/05
I did not get under to see if it was the four plug trans but I understand there is a good chance it is based on date code.
Anyhow, I may run away depending on what others say here about this issue.
When decelerating, brake on or off, it does a hard downshift at about 52kph (about 32mph) I think this is coming from 4 to 3 not sure but its a good clunk, can feel it in the seat... Easy to reproduce so I did it over and over trying to see if it was driveline or what. Always at the same speed, easiest way to test was going up a slight hill, at say 70kph as long as we got to high gear - let off the gas and let it decel to about 50kph.
does not do this when manually downshifting.
All upshifts are smooth. Has a slight bit of 'clunk' going from reverse to drive, slight enough to ignore... suspect a ujoint but planning another visit to check things if this is something that can be reasonably fixed.
Any ideas on this?
Thanx

 

[JustSumDad]

Some peeps on other info sources are indicating that maybe the shift solenoid is the cause, or a sticky valve.
I wonder if a sticky valve would cause such a specific speed that can be so easily be reproduced.

Hope someone with good A.T. knowledge on these can chime in

 

[65Corvair]

I am not a transmission expert, but the clunk from reverse to drive may be the upper ball joint (#2) or rubber bushing (#1) in the rear upper control arm.

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[KJowner]

The thump from the rear upper arm is very noticeable but it should happen at any speed when you accelerate or slow down, the specific speed mentioned sounds more gearbox to me, but the arm is a cheaper option so worth a look.