Whoa... Wait a minute. You may want to spend some time with your owners manual
There should be 2 buttons on your ATX shift knob. The large thumb button sticking out of the left side of the T shifter is the reverse lock out button. You have to press on the brake pedal and push this button to move the shifter from Park to R or D. You also can't go from D to R without pressing this button. (Reverse LOCK out...)
The overdrive button is smaller and is a little lower down on the shift handle. Mine is sort of a green color. When you press this and release it, the "OD off" light should turn on. Press it again and the light should turn off. If you don't touch this button the light should not be lit up when you start the car.
A new tranny will cost you over $2000 probably. Might want to spend a little time checking fuses and fluid levels etc. before jumping into a tranny replacement.