Car is auto and has 184,000 miles. Just started being difficult to manually downshift from D to 3rd. Won't go from 3rd to 2nd while moving. While stopped can get in 2nd and car is then in gear and will move. When stopped and shift into 1st it will not stay in first, shifter just moves up to 2nd gate. Any suggestions where to start? Linkage? Transmission seems to operate normally by its self while in D or R. Tia.