Sounds like it's going into "Limp-in". The transmission has input and output speed sensors. When slippage is detected between them, the computer shuts the electronic system down. You will have a choice of hydraulically-controlled 2nd gear, neutral, reverse, and park. When it goes into limp-in, it drops to second gear. That's why the engine speeds up.
The transmission will need to be replaced or rebuilt, but you can overcome the problem temporarily with a little driving technique. Since you already noticed the problem occurs when shifting into overdrive, when it's about to shift, speed up a little more than normal, then let off the accelerator and allow it to upshift. By letting off the gas, there will be very little torque so no slippage will occur. Once solidly in gear, you can drive like normal until it has to downshift again. This will buy you some time, possibly weeks or months, but eventually the slippage will get worse.
The computer constantly updates the shift points to mask the normal clutch plate wear. The advantage is nice crisp shifts over the life of the transmission. The disadvantage is you are not aware of the normal gradual wear, as you were in older cars, until the wear is so severe, you have the condition you're experiencing. Said differently, you just have no warning that normal wear is taking place.
Sunday, November 29th, 2009 AT 7:14 PM