||If its stuck in second gear not first, no shifting at all other than reverse and park then we look at speed sensor, wiring harness. Four things are main suspects. Chassis to trans ground, main conector plug and wiring harnes at the trans, speed sensor ro sender. Finally there is probably a device in the dash called a drak (Have no idea why) It takes the speed sensor signaal and changes it into what each computer needs including the spedometer and cruise control.
If it shifts first second then we are looking inside the trans for bad harnesses, bad conections, bad solinoids, and jammed hydraulic valves. Try banging the throttle full on and of hard. That may clear a stuck valve. All this is accessed through the oil pan.