I've never driven an old Volkswagen that wasn't somehow like trying to shift a baseball bat in a barrel of coconuts. With a good transmission linkage, the shifting is acceptable, but never fast and crisp. With worn out transmission linkage, these cars are practically impossible to drive.
I'm not tying to be an ass, but resign yourself to the fact that you own a 30 year old economy car. Remember, these were cheap cars back in the day. It's not going to drive like a sportscar. There are simply too many moving parts and bushings in the linkage on these, to ever get quick, fast shifting. I also read somewhere, that when VW designed the mk1, they had one design/engineering team work on the body, another do the transmission and then somebody else was tasked with the job of somehow coming up with a way to shift gears in the thing. And, I believe it, there's no coherency. The mk2s are just a little better.
Onto your problem, I think the car (or truck as you have it) body may be part of your problem. The geometry isn't the same as when it was new, especially if the truck had any fender-benders in it's life, so if you're adjusting the linkage in accordance with the instructions for a new vehicle, it may not work as intended. That's one thing that frustrates me about these, the chassis isn't very rigid, the doors, hood and hatch on my car require routine realignment (about once every year).