update: got the sensor out needed a pry bar, then needed a mallet hammer to put it back in. put two quarts of friction modified syncromesh. so far it hasn't popped out of 3rd gear, only drove to oil recycle place. before gear oil change, popped out twice going to recycle. so will see. of course now speedometer doesn't work and engine light popped on. so need to order and install a new speed sensor. I know it is .3 quarts short on gear oil. about 2 1/3 qt. came out of there.

 

Just add the 1/3 of a quart you're short when you change the sensor.You'll have it out anyway.

 

after putting gm syncromesh in trans through speed sensor hole (which solved 3rd gear popping out issue completely) speed sensor hasn't worked since, ordered new sensor from amazon prime $13 one day delivery. still no go, but only one code with the new one 720, the old one had many codes. went to dealership, noticed on diagram washer goes on the motor side of sensor, I think this helps with grounding the sensor and setting the gap (gear to sensor). I lost the washer or put it on wrong side, shortly going to get another washer. and test.

 

tested sensor, i could see teeth marks where i tapped it in, took off o-ring , sensor wouldn't fit. so sanded plastic down until it fit. put back on o-ring . still no go. ordered another sensor. 38$ amazon prime, one day delivery, so should install it around 3, fingers crossed. going to take off o-ring to make sure it fits. if it doesn't going to sand it down till it fits.

 

sensor came in sanded the plastic a little, tried a with a washer as spacer, no go, then tried with washer half the width, no go. then put it in with no washer, its a go I have working speedo, cruise control and odometer.

 

Awesome! Thanks for the update. The best part is you ended up spending a heck of a lot less money and time versus rebuilding your transmission.