The O2 sensors screw into a threaded "bung" welded into the exhaust.
There is usually more than one on newer cars, an upstream (located before CAT) and downstream (located after CAT).
Use a penetrant like PB BLaster and soak the threads of the O2 sensor overnight. Unplug the electrical connector, use a wrench to remove the sensor.
The new sensor should be coated with antisieze, if not buy some and put a little on the threads (do not install the O2 sensor dry).
Having said all that, I think your problem stems from the trans. Shop. They either installed it wrong or forgot some connections. It sounds like the torque convertor lock up mechanisim is not releasing.
If the engine was running fine before the trans. Repair then I would insist the trans. Shop repair it.
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Wednesday, September 24th, 2008 AT 9:26 AM