I picked up a 91 626 DX a few weekends ago, and I have been having a few wierd issues with the trans. The other day, after a hot commute home, I checked the fluid and it had bubbled all the way to the top of the dipstick. I checked it awhile later, and the fluid looked over 1/2" high, so I siphoned a quart out. Then, driving home today, the trans kept bouncing off OD like it wouldn't quite get in. I stopped and checked the fluid, and it looked low, like at the bottom of the cold area. So I put a half quart back in.

Ok, so, number one, are these transmissions THAT sensitive to fluid level, and number two, these dipsticks are hard to read. There is fluid all over the stick, so it's impossible to see exactly where the level is. The fluid is a good cranberry color, and does not smell burned. Also, NO FLASHING LIGHTS. HELP!!!

 

I actually think it's in od when it starts lurching, always around 60. Just a slight repetitive jump, but I can see that tach is not moving, and no cel or trans lights.

 

At least you got one w/the "good" auto trans. The later ones are a nightmare of problems from what I understand.

Personally, and before any damage is done to it, I would take the car to shop that knows auto transmissions.
It may just be that it needs a thorough flush and refill. I mean it sounds like something may be clogged or sticky in there to me.
Or it could be a valve or sensor problem, but don't mess around with it. Prevetion is the name of the game here... especially with an older car. Much cheaper to fix now than later. I'm sure you wouldn't want to have to pay for a trans rebuild.