904 2nd gear stucking? Pls, help!

I finally had a change to drive my Dart. 8)
I had rebuilt this tranny about 4 or 5 years ago, but never before used it.
Now, when i reversed the car out of garage, the tranny felt good. Except it was hard to drive slowly out of the garage, cos it spinned wheels pretty easily. :)
Head to the dirt track/test road. First gear felt good, but actually I expected little more slipping on tranny, but only that was slipping was rear tires. :)
Well, i floored it, but soon when I was expecting the 1st->2nd change, it felt like tranny jammed and rear tires stopped spinning, then it was 1st gear again. Little more careful accelerating, and it happened again.

Friend told me that band adjustment may not help in this problem, but didnt have time to explain... :(

Please, tell me, if anyone could know if I might did something wrong when I rebuilt this 904? Or could lying in garage without oil cause something to jam and make this happen? I've never even heard about anything like this, nor does my Finnish friends. :(

-LionStab- ;)

PS:It was first time ever I tried to rebuild automatic trans, and the result was pretty much expected.