[TR] slipping out of third

[Peter Arakelian]

I have a 71 TR6 non-overdrive transmission. When I am in third, decelerating
down hill, on occasion, it will slip out of gear. Not pop out, but
occasionally slide out - it feels like I just stepped on the clutch.  No other
problems with transmission.  Goes through all gears fine - up and down.  No
noise, no grinding.  Only the occasional slide out of third.
Diagnosis?

Peter Arakelian