That sounds a lot like what my clutch/transmission did. It was almost like the tranny fluid had been replaced with peanut butter. Very difficult to shift from one gear to another. Only mine was from first to second... on the same rail in the transmission.

Mine ended up being a cracked syncromesh gear and worn out clutch. But ultimately the cracked syncro was the hard shifting problem.

Search for a post that I started about my transmission troubles. I think I included pictures of the crack and other carnage...