1999 Ford Ranger trans not shifting all the time

Yesterday I started driving and the car. Would not shift out of ist gear. I came home and used another car.A little later my dad took it out and it did the same but them stared working fine. Also when its not shifting right the speedometer is not working.I changed the filter and fluid but that didnt help sometimes it works fine then while your driving along itdoes the same also when it acted up the overdrive light starts blinking. Can use some help thanks