When it was stuck, did you try and bump the throttle while holding slight pressure on the shifter when slowing down.

If it works fine that way, then I would look at the clutch and slave cylinder, if not then looking at linkage and trans.

Shifting out of gear without the clutch only works when the engine and the drivetrain is in sync and not having pressure locked on the gears.
when you hit the sweet spot it will slide out every time.
When I am coming to a stop in mine, what I always do.

Same way on a trans in a semi, you don't use the clutch.