Loud clunk, tranny goes into neutral

Well, let me start out by saying when this happened it scared the living shtt out of me

I was in first gear turning out of o'reily's autoparts, when i get going there is this loud ass clunk sound and the car revs up like its in neutral, this has happened twice in one week, i think the verdict might be going down a pretty big curb and somehow it kicks it out of first and into neutral (maybe it wasn't in gear all the way in the first place ) Could it be b/c my stop bolts on my tri-ax are keeping me from being all the way in gear?? I'll check that tommorow.

all help is welcome and very, very appreciated.

Thanks,
Patrick

By the way, my clutch doensn't slip, so thats not the verdict