1995 Paseo Overdrive Problem?

[Milambyr]

Howdy,
I've got kind of a lenghty post but want to be as descript as possible, I really need advice.

I have a '95 paseo with about 140,000 miles on it and started having this problem with the overdrive (I think). The problem is it doesn't switch gears like it is supposed to, around 30-45 miles per hour it won't switch into the next gear and uses way to high RPM's (i want to say around 3-4 thousand). Now, sometimes when I gun the car and accelerate extremely fast from 0 - 30, it does switch into the overdrive gear at around 30 miles per hour and the RPM's at the speed i mentioned before go way down and it runs smoother until I turn the car off.
Note my overdrive is ALWAYS on, it just doesn't seem to want to work. Also, when I turn the overdrive off, nothing happens 90% of the time. When I do get overdrive to work and i turn it off, you can tell it's working because it gets out of that gear and the RPM's will shoot up.
What is wrong with my overdrive? I know nothing about transmissions as compared to engines but I can't figure out if it might be a transmission problem or is the computer just not getting the signal to turn it on or what? Any help is greatly appreciated, i'd like to fix this ASAP as the rest of the car is in great condition.
Thanks!

[Quadancer]

Did you ever find out what it was? Mine is doing the same things.