help please

i have a 91 rs with a 305 would i have the on board diagnostic system because when it goes from 1st to 2nd it sounds like it slipping but my speed opt dont jump but the tack go up high all the time but never hit the red well mabe when i hit 100

try getting a fluid flush , that's the best thing that can help without an overhaul. Maybe it's your torque convertor.