Shifting issues

Got the bike, a '74, on the road after a 6 year rebuild, and I'm having a few issues with shifting. I've already double checked the primary tension, and played with clutch adjustments. I think that when I get the chance (hoping this weekend) I'm going to have to open up at least the outer cover. Until then, I figure I'd check in with the pro's to see if it's something that has been experienced before.

Shifting from N to first is easy, as is up shifting through 4th. The problem sets in when I decide to downshift. Not everytime, but often when I pull up on the shifter, nothing. It moves against the spring about a half inch, but then just stops. It's not that it needs to be forced harder, it's more like it's up against a stop, similar to if you have it in first, and would try to pull up on the lever. I can get the shifter to engage by kind of wedging my foot in between the shifter and the foot rest while pulling up on it, but not normally.

Let me know if you have any ideas, and hopefully I will get at it before the waiting drives me crazy .

Check the spring and pawl inside the transmission cover. I have had issues with them and the shifting.

Yeah, what Brent said. That spring can be a fussy little pig if not installed right and with the proper tension.
I am assuming you went into the gear box during this rebuild?
Good thing is that if it is the spring, you only have 1 cover to remove.