I have the same problem with the shifts since I got the adjustments on the cable and modulator pressure correct.
I'm going to measure the vacuum supplied to the modulator as soon as I recieve my gauge next week.
A quick check makes me suspect I have some sort of problem with the vacuumvalve on the IP because it seems to be totally insensitive of adjustments but I'm not sure yet.
I quoted a new one from the dealer and it was about 75USD so I think I might get one from the junkyard for comparing mine with.
My car does not have the transducer, only a green check valve directly inline with the modulator but the valve on the IP works the same way.
Let us know what you find and I'll do the same.
MB E300TDT -98