Need help diagnosing tranny problem.

[THATDONFC]

Yesterday I was driving and I saw an open road so I decided to take it. I was at WOT and when I was about to shift from second to third the the shifter "popped" out of second gear. I heard a loud clunk. Then it happened once more an hour or two later. What could this be??? Could it be a sign of my tranny going out?

[IronButt II]

First thing I'd check is tranny mounts and motor mounts. If the motor and gearbox are flopping around under there... that can certainly cause your problem.