Kevin,
It sounds like the linkage is out of alignment.  I just went through the 
drill on my 81 so the memory of it is still fresh.

Pull the boot at the base of the shift lever up and off and check to see 
that the two holes in the base plate and below are lined up.  If not then 
loosen the two phillips heads screws and realign things then tighten down 
on the screws.  

Then drop the spare tire and check that the gap between the tang on the 
bottom of the shift mechanism and the side of the housing is around 19 
mm.  It should be ok, but if not write back to me and I'll dig out the 
procedure for adjusting it.

Then go back to the tranny and make sure that everything is nicely 
greased there where the two vertical plastic balls fit into their cage 
(you'll see what I mean when you look back there).  One thing I had a 
problem with was the guide ring on the shaft that protrudes from the 
tranny into the shift rod that attaches to the linkage up front.  If 
that's missing it'll through everything out of whack.  Undo the big nut 
at the end of the guide shaft and check that the ring sits in the 
depression at the other end.  If not you'll need to get another from the 
dealer.  Lube the ring as well as the shaft that fits over it and get 
everything tight again.

If the above doesn't solve your problem then the tranny is suspect and I 
can't help you much there.  But the above checks will solve 90% of 
shifting problems if the tranny's ok.

Write me with any questions, I'm glad to help.

Jack