Have you tried lubricating all the shifter linkage?   My vanny shifts much
easier every time I squirt some spray lube on all the moving parts of the
shifting linkage.  I lube everthing whenever I have to go under the
van...usually about once a month anyhow..
   Also, there is a kit to replace the wear-prone parts...It's been a long
time since I got my Vanagon but I got that kit when I first got the van...I
don't recall it being really hard to shift, but it was not what I liked and
I was replacing all kinds of parts at the time, so I did that, too...

   You could also have clutch issues...