I'm a pretty good at figuring transmissions out, but I'm stupmed on this one. The car is a 93 850 auto; 285k on the car; 130k on the engine; about 110k on the trans.

When accelerating LIGHTLY on a slightly downhill grade (~2%) while the car is cold, the engine speed will surge slightly between 3rd and 4th gear. Light acceleration means about 1.5-2 on a scale of 5. The car needs to be going slightly downhill - so gravity is causing some pull. By "surge" I mean that as the transmission is making the 3-4 shift, the engine speed will rev up about 500 rpm before it completes the shift into 4th.

I'm thinking that the ECU is thinking that it is a very light shift, so it makes the 3-4 very softly, allowing more slippage. But a 500 rpm jump seems like it could be a sign of trouble. I've also thought that I'm noticing the torque convertor locking up more than teh actual 3-4 shift. The way they programmed the torque convertor drives me nuts! It's like a Ford!

It does not make the rpm jump neither under lighter throttle nor heavier throttle; only at a certain amount of light throttle. It also is just fine once the car warms up.

I'd deeply appreciate anyone's thoughts on this noodle teaser.

Oh, yeah. I've also run about 20 quarts of ATF through the trans. I ran 10 through when I bought the car and another 10 after about 3k. Both flushes produced pretty murky, brown fluid.

Am I screwed?