2nd, 4th, 6th, and reverse gears "sticky"

[Zentelis]

The 2nd, 4th, 6th, and reverse gears have been "tight" the past few months. Tonight it seemed worse. I had to push pretty hard to get them all the way in gear. And when I shift out, I have to push pretty hard as well. They feel like they're "stuck" in gear until I apply enough pressure. It almost feels like I'm shifting into and out-of a blob of tar.
1st, 3rd, and 5th are perfectly normal, leading me to believe (and desperately hope) that it's just the shift-linkage that needs adjusting.
Any thoughts? Something I should look for before I pull the transmission apart?
Thanks, folks