904 misbehavin'

Finally got the ragtop out and ran about 80 miles the other day. At 50 miles or so, the trans was balky at shifting into 3rd. I put it in neutral, blipped the throttle and went back to drive. The tranny went into 3rd just fine. For the rest of the ride, the 2nd - 3rd shift was a maybe, but the procedure I mentioned worked. I'm worried. Anyone have thoughts about this behavior and how to fix it? Thanks!

ATB

BC