Arthur, I spend quite some time on making the transmission work properly with my mechanic. What I did wwas all that was advised to you here in the posts from the fellow Members plus a couple of more things. As an amateur, what I would advise is as follows:
I would start with replacing the fluid and filters. You probably do not know how many kilometers ago this was done. (Mike)
1. Study the Technical Manual on how the transmission solenoid should work and check it (Shvegel)
2. Check the linkage to make sure the throttle switch is properly adjusted - you will find adjustment procedure on the forum (ja17)
3. These two above are interdependent - throttle switch is steering the solenoid, which, in turn, is responsible for fluid pressure and shifts, they need to work correctly
4. I would check the pressure in the gearbox - you have the procedure and data here on the forum, it is a relatively simple thing, just make sure you do not confuse the pressure units. You will need a gauge, a banjo connector and a little self made tool - your mechanic has that. If your tranny shifts bad when cold and better when warm - maybe you are on the edge of required pressure and just need to adjust it.
Please note that you should have engine linkage ok so that the idle is ok, to have vacuum ok so that the transmission works properly. It is all more interdependent that it seems, e.g. brake booster goes bad - no good shifting.
When I started working on my transmission - I read all I could through "search" on the forum, read all in Technical Manual, wrote the procedures in Polish for my mechanic and it worked. I think you have more knowledgeable mechanic there, so it will be easier.
