No 3rd Gear (2000 automatic)

Looking for some advice on my 2000 Dakota. Its a 4.7L and a 4x4, and I have owned it since new. Think I've taken pretty good care of it, and its never given me any problem in 130K miles.

Tranny never acted up until the other day, when all of a sudden I had no 3rd gear. Check engine light is also now on. Shifts fine from 1st to 2nd, and then stays in 2nd gear until I get up to about 65mph. At 65 it shifts into 4th and then locks up the converter. It also now seems to have more engine braking when I take my foot off the gas??

Haven't driven it much since it began acting up. Plan to pull the ECM Codes and also change fluid & filter, but was wondering if anyone had a clue as to what might be wrong. Is there a Solenoid that controls 3rd gear that may have gone bad? Any clues or advice would be appreciated. Thx

I did pull the Check Engine Code, and its P0720, pointing toward the Output Speed Sensor. I am assuming this would give me the symptoms I am experiencing

am posting this in case my success can help others..........I put in a new Output Speed Sensor last night ($40 part at the dealer) and it fixed my problem. My trans shifts like a dream again.