Mitsubishi Repair: 94 Galant Transmission problems:, mitsubishi galant, gear ratios

Question
I have a 1994 Mitsubishi Galant ES with automatic transmission; The problem is that it shifts great 1st 2nd and 3rd gears but doesn't get 4th gear (RPM's stay high and don't go back down.)And if I try to click the Overdrive the RPM's just race up really high so I guess O/D doesn't work. The transmission feels smooth and gets good but just up to 3rd so hopefully it doesn't require a new transmission. I just flushed it, put new oil, and new filter 2 days ago and saw no improvement. Is there a good fix I can do so as to not have to replace it? (ie. adjust gear ratios, replace ECM or TCM, or if a mechanical problem what parts should I replace or adjust in transmission?)

Answer
Danny,
Unless you have experience in working on internal components on Japanese auto transmissions, this job may best be left to a professional.  Your problem could be a bad TCM, but its best to have that checked before having a mechanic get into your transmission.

If your problem is mechanical, it may be a kickdown servo, bands, or even your gears.  I would only recommend a transmission shop to get into your transmission to inspect it for mechanical problems.
Good luck!