C6 won't downshift when stopped

[rattle_snake]

After 3000 miles of expected behavior the trans will stay in 3rd gear after a stop. Have to manually shift to 1 to get it in 1st. Upshifts fine. Downshifts as expected with shifter. Hot or cold.

Fluid is clean and smells ok.
Level is full.
Vac line is connected to modulator
Kickdown is properly adjusted

After some digging sounds like governor sticking.

 

[Johnny Longrifle]

Could be the governor. Throw it in park while you're moving 30mph, for 5 or 6 seconds. Do that a few times and see what happens.

The park pawl bouncing on the output shaft will sometimes loosen any crud that might be in there.

 

[Pony_Driver]

That's one way to try it.

 

[Johnny Longrifle]

I know it sounds suspicious... But I swear it works.

 

[rattle_snake]

Just to follow up, pulled pan, the trans is full of shaving and is fucked as I suspected.