I have a 1980 300cd W123. I have been trying to get the automatic trans to shift properly. I purchased the books from Mercedesource about tuning the automatic trans. I have gone through all the procedures described in the manual with little if any success. The symptoms are early shifts, flairing between 2nd and 3rd gear, slipping into 4th gear, and no kick down. The trans ****s better when manually shifted. Reverse works fine. Trans will drop down into first when starting out if accelerator is floored. As a side note the vacuum pump is at 18 inches of vacuum. I have rebuilt it and the vacuum came up from 14 to 18.

Below I have listed everything I have done to the trans.
1. replaced the front seals (pump and input shaft)
2. replaced the filter and added synthetic ATF. Also drained the torque converter fluid.
3. Checked and replaced the vacuum modulator with a new one found on e bay (red color for the 1980 722.1 trans.)
4 After adjusting the modulator to stock pressure and having the vacuum line off and plugged, the trans shifted early and flared in 2nd and 3rd gear. Same problems
5. re-adjusted the modulator pressure up so the trans. shifted at high RPM with hard shifts, no slipping and no flaring. The trans would also kick down if accelerator pushed to the floor with the vacuum line disconnected. When the vacuum line was re-connected again the early shifts, flaring and no kick down were back.
6. Installed various colored vacuum line orifices ending up with the green on (smallest orifice) with little or no changes to shifting with different orifice sizes.

Questions:
Is my trans just worn out with 253K miles on it? Would it be better to swap the trans out to a later one with a Bowden Cable connecting to the accelerator linkage (this year trans has no mechanical connection to the accelerator linkage at all. Appears to be a one year only configuration).
Any help would be great. I love the car but want it to shift correctly. I'm at my wits end. What should I do?

Thanks

Warren