Subaru Repair: 98 Forester Transmission Going?, shift into overdrive, rear differential

Question
For the past week my 98 Forester S with an Automatic Transmission(95k) has been giving me some issues on start up. When I start the car and begin driving the RPMs in each gear. First gear races wheel above 3500, then 4000-4500 for the rest of the gears. It won't shift into Overdrive. When I stop at a stop sign the vehicle shakes violently and stalls, unless I put it in park before it stalls. If I park the vehicle and turn it on and off a few times the vehicle drive like normal. I can drive the vehicle 500 feet and restart the vehicle a few times and it works, so I don't think it has anything to do with the engine or transmission "heating up"

I brought it in the shop and of course it didn't happen so that was useless. The thought it might be the Torque converter starting to lock up which would mean a complete rebuild of the tranny. I'm not sure if it is worth pursuing the rebuild or just getting a newer vehicle. I still owe about $4500 on the vehicle if that makes a difference. It has received about $2000-3000 worth of work in the past year(new cam seals, spark plugs, spark plug wires, new AC compressor, new rear differential), luckily most of it was under warrantee. The warrantee ran out 2 weeks ago.

I really appreciate your time and look forward to your insight.

Answer
It could be several different things. Has the Check engine light come on? I would have someone look at it. Thats something I can't do from here. You may need to leave car overnight with shop to try and duplicate the concern if it happens cold. As far as trading it in, that's completly up to you, You have already put alot of money into this car already. How much more is the car worth? Thats the question you will need to answer.