Thanks for your help!!!
I ordered an OSS sensor because I had removed it an saw some fine metal on it and crack across the epoxy. This is the forward OSS on the tail shaft. Put the new one in and still the speedo quicks after a mile
I also noticed there is another OSS behind the 4x4 shift motor, so I put the sensor there since I was getting a 720 code. Same crap. The 720 clearly points to the OSS
So I'm now
after waiting for the sensor and it still not working.
I recalled your post, and took out the sensor from the rear axle. It was coated with some fine metal. Cleaned it off and the speedo now works! Well at least for the last 25 miles.