Chevrolet Blazer Transmission Overdrive

Won't Shift Into Overdrive Causing Poor Mileage Due To A Higher Rpm. Could This Be A Sensor Problem?

I Was Driving To Work And Everyting Was Fine Then All Of A Sudden Third Gear And Overdrive Quit Pulling , I Can Shift Manually And Feel The...

Had To Replace Radiator, While The Transmission And Oil Lines Were Disconnected The Motor Was Started And Put Into Gear For Less Than 5...