aw4 trans slipping....?

odd series of events here - just tossing this out to see if anyone has had a similar event...

tranny started slipping at highway speed, checked fluid and none registered. very odd as there was no sign of leakage and I had checked it recently.
anyway, added a liter and now registered on the dipstick so away I go. still slips off and on, so I add another litre. climb a steep hill on highway, 3rd gear about 90kms/hr and I see nasty amounts of smoke behind. ohoh! pull over and I see that it's just fluid coming out the filler tube and dripping on the exhaust pipe. check the fluid level and it is way over full now....WTF??
didn't have any more slippage problems from that point on - about another 140kms...

I am guessing that something was plugged in the tranny and kept the fluid 'stuck' in a part of the tranny, not in the pan. when I added the fluid in 'unstuck' it and all started circulating again.

Any comments/ideas/btdt on this?
btw, I'm just running 235/75/15 tires on a stock drivetrain.

i believe that you're supposed to check the fluid at idle when its in its operating temperature, not when cold. so you might have filled it cold and when it gets hot it spilled over.

sorry, I should have been more specific

- when I checked the fluid level it was definitely at operating temp - the first time (when nothing showed) was after driving about 600kms with just a brief stop after the first 400kms.

susequent times were after driving at least 20- 30kms at highway speed

Hmm your guess is as good as mine thats really odd. maybe someone else could chime in here as to what might have happened.