Using Oil, Overheating and Mis-shifting

[shajck]

My car is having several problems and nobody is able to find the problem. It's started using oil about 1 qt/1000 miles. There is no mark where I park, nothing in the tailpipe, no oil in the antifreeze, and no smoke.

In May this year, while in Chicago traffic, the temp light came on. I turned it off for a while and preceeded to drive with the heater on. Freeway driving ~180/190. Easily goes over 210 without a problem and I've turned the heater on inside the car when it gets to 210 so I don't know if it will go higher.

When I have the AC on and it's not hot outside, the car has reduced power and accelerating the AC air warms up until I reach a constant speed. When the car temp goes high, I turn it off.

Yesterday after not driving my car for a couple of days, it would not shift properly. First it would not shift, then very hard and then out of gear. It finally did shift and would shift hard. I had it towed to a shop instead of driving it.

They cannot find anything wrong with it and this is not the first shop!

Please offer suggestions on what's going on here. I'm concerned about using so much oil and the overheating more than the shifting problem. Is there a computer that could be failing to cause these problems, yet no codes and no CE light? Earlier this year a oxygen sensor I was told needing replacing. They said not replacing it would not cause a problem. Could that be what's going on?

All suggestions are welcome!