87 tranny wont shift

My sister has an 87 with a 3.8L. I drove it and it shifts into reverse, neutral and drive but will not upshift out of first. I do not know what could be the problem. I know she needs the filter and fluids changed but I think it is a sensor or module gone bad any help on this matter would be apprectiated. Thanks

check the tv cable it mybe stuck on wide open