Try cleaning out all the tee's and orifices in your vacuum system.
Also, I would work on getting the vehicle to run as well as possible.
My experience (limited) with these vehicles is that as you get the car to run better and better, the shifting kinda comes along with it.
But, getting the vacuum to work properly is essential to good shifting,
there are numerous excellent threads about vacuum system.
Also, there is the Bowden cable that may or may not be an issue.
All things are interrelated on these cars, so don't take a huge swing at it right off, but work on getting as many neglected maintenance issues corrected first, and the smoke. Tried a compression test yet?