91tutone

This is a stock 91 RS I've owned the car for 10 years no motor modifications done about 155000 miles . I seem to be having a problem with no overdrive, trans shifts smoothly 1st to 2nd 2nd to 3rd but feels like no kickdown and no overdrive. I've also adjusted the TV cable or Denton cable to stock specifications. Every place I've talked to about taking the car they tell me a hundred and fifty thousand miles I might as well just rebuild the tranny. I have replace trans filter tcc . Any info or advice would be greatly appreciated.