Gee's i've found out one too many things the hard way. It's more than likely your syncros. Mine did the same thing going from 1st into 2nd. Over time (a month or so) it got progressivly worse until one day i heard BANG and i was SOL on the freeway. I highly reccomend taking it to a tranny shop and have it freshened up w/some new syncros, as i'm pretty sure you can still find them, and some heavier gears (if you've got the $$$) Or you could try and locate a use tranny, but they are hard to come by.
P.S. if you do follow thru w/ this you should almost def. upgarde to a 9lb. fidanzza flywheel & a stronger clutch. I personally have have a stg 3 from clutchmasters w/ the fidanzza flywheel and the difference is one you can feel!!!