So here is what I have done to attempt to get to the bottom of my hard shifting trans. Symptoms are hard shifts, especially 1-2 and 2-3 at all temps, especially on smooth roads, at all acceleration speeds.

1.) replaced all the vac connectors and half the hoses in the engine compartment
2.) checked all the orifices (all were carbon/blockage free)
3.) replaced a leaking vac pump check valve at the vac pump
4.) replaced a leaking AC vac element
5.) replaced a leaking AT modulator cap
6.) replaced the differential mount (a stretch, I know, but it needed to be replaced)
7.) replaced both vac switchover valves in engine compartment
8.) reconnected overboost protection circuit
9.) disconnected the EGR/Recirc circuits from the system
10.) changed AT fluid and filter to mobil 1
11.) changed diff fluid to mobil 1
12.) changed the 50 degree switch (old one was dinged)

13.) performed the following tests
- got +/- 20" of vac off the distributer
- loose less than 1" of vac per minute in entire system
- no real vac leaks in any of the circuits as far as I can tell
- modulator holds vac with no leaks at all
- watched vacuum applied to vac control valve go to zero as linkage is pushed forward.


14.) next step - connect tester to TRANS output from vac amp and watch pressure at modulator while driving

It seems to me, the failing component must be one or more of the modulator, the vac amp or the vacuum control valve.

Let me know if you have any other ideas about specific tests for those components.

thanks

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