Transmission wont shift into overdrive

What is your question?

3.7L V6, Lithonia, GA, February 26, 2015, 10:15 Rookie Vehicle pulls very well in lower gears but will not sink into Drive/Overdrive when it should. I have pulled and installed a different tranny, as well as torque converters. Im thinking i may have a sensor problem but not at all sure. Any Ideas.