I had this exact same issue. Replaced speed sensor from the top of the rear differencial ($20), unhooked then rehooked the battery and all was well.

These threads are invaluable for solutions.

 

I know this thread is old but I think its worthwhile to answer for the next guy who has this issue. Had this very same problem but also a low rpm shudder. No engine codes were showing. Long story very short, it could be a minor misfire like I had. Took it to a mechanic with a good scanner and he checked my code history and it showed a misfire on #8. Went home, replaced the coil, used the compressor to blow out all of the dust that accumulated over the years and problem was solved. I had mechanics go right into saying various sensors inside the tranny or needs to be rebuilt at $2,400....$50 for the coil and all is well - thanks mainly to forums like this where another guy had this same issue.

 

In the end, I found a guy here locally in business for 36 years who just swapped a whole-nother rebuilt trans in for 1800 out the door. I had him do a little extra work while he was down there so it cost a little extra on top of that. But not a bad deal. Oh and it came with a one year warranty. I've had it back in my hands over a month now and have had no problems.

 

Replaced the sensor in the rear axle, but that wasn't the problem. I replaced both batteries (which starting getting very weak) and that fixed it. Not one code since then
Made a little sense to me hearing on here somewhere that the trans sensors are especially sensitive to voltage

 

It sounds like this problem can manifest from multiple issues. I basically changed out both sensors, both batteries, the computer, and then all that to find out that it was a wiring issue. Water collected in a connector, corroded some wiring, and to do some replacing and all is good now.

 

i tried all the same stuff as you then i saw another post for someone having the same problem and he said he ran a ground from the engine to negative battery cable. I done this and the o/d isnt flashing in reverse now i'm going to drive for a while and see what happens but it seems like it may have fixed the issues....

 

the P0720- output shaft speed sensor, the O/D light flashed
I fixed it by replacing a spark plug coil, the dealer say sometimes they throw off a r f signal that interferes with the electronics