98 Contour's automatic transimission is not engaging forward gears.

At first,transmission seemed to take time in warming up and engaging gears. Had to resort to shifting manually. It would rev high and then accept shifts from 1 to 2 to D, sometimes it would grab D but usually after about 1/2+ mile driving.

Drained, flushed and changed tranny oil yesterday. Now it barely grabs first and is revving more freely than actually moving vehicle. Reverse works fine. Fluid level seems fine, no leaks.

Is there a sensor problem? Or I am I looking at something more terminal?