Hard shift high to low range

[Mrkentee]

Eaton 13 speed trans:
When shifting from high range to low range it sometimes, not always, slams into low range. But:
1. It only happens when the weather gets warmer, like now.
2. Only from high to low. Shifts fine going up.
3. Only if speed is between about 9 mph up to 15 mph. I don't use low range over 15 mph.
If I slow down to 5 or 6 mph, it doesn't do it.

I'm replacing the filter/regulator. It's cheap enough, $50.
Other than that it could be synchros.

Any ideas?