Please help! tranny problem?

I have a 99 Subaru Forester with on 84,000 miles. When I am coming down steep hills and I press the brake, the car (aggressively) downshifts to 3rd gear and the rpm’s rev to 4000. It doesn’t matter if I press on the gas, coast, hold the brake, it will not upshift. Usually, when I reach the bottom of the hill and begin another incline will it up shift. So I have taken to pulling over and begining from 0. Then it works fine until we go down the next hill. This only happens at high speeds and for relatively steep terrain. Also, when engine is cold shifting from 2 to 3 cause a little stall, rpm rev, and jolt. And sometimes when going up a hill shifting feel loose and engine will rev while shifting. It doesn’t always feel like it is shifting at the right time… Not sure if these are all different problems (and different fixes) or if the problems may be related (hope, hope!). Thanks for any insight. I really want to be able to leave this valley and not worry… Also a mechanic mentioned the lockup torque converter(whatever that is…)

When you checked the transmission distick, was the level normal?
How about the color and odor of the fluid?
When was the fluid (and filter) last changed?

I believe that is just what it should do.

A bad torque converter is a pretty good guess, actually.
This sounds like a vacuum problem, and it certainly is not normal. In fact, the transmission is reacting to hills in reverse: it should be freewheeling downhill automatically, in the highest gear. The gear shift provides a manual method to downshift to allow the driver to engage lower gears if necessary (and when descending very steep hills, you should manually downshift early on, at reduced speeds, to prevent overheating the brakes). Conversely, the auto transmission should tend to downshift when the car is climbing a steep hill, to provide torque.
I think the mechanic told you it was either a blocked torque converter or a locked torque converter.
I do think all of your problems are related, and for your sake I hope the mechanic is right, that it is a bad torque converter. But before he does replace that part, ask him to check for a vacuum leak. If may be that your transmission is guided by vacuum to know when to shift to which gear. If so, a vacuum leak fits your problems pretty well.