1995 Isuzu Trooper transmission problem

I have 1995 trooper auto 4x4 ls. When I drive it the transsmission is just find for anywhere from 1 mile to 150 miles. Then all of the sudden the transmission light comes on and it drives just fine until I come to a complete stop. Then when I begin to move it act like its underload if I leave in overdirve until it gets out of first gear then its back to normal shifting and downshifting till I come to a complete stop(the light is still flashing) or I can manually shift it from first and it is just fine. If I turn the car off and restart it the light will not be on and then at sometime the light will then come on. Please help as I reallylike this vehicle