Transmission Issue or Speedometer Cable?

I have a 1996 Escort 1.9 automatic trans. Over the weekend I changed all four motor mounts as they were past bad and the vibrations under my seat were getting too much. I had the transmission rebuild about 6 months ago and asked the shop to check the mounts but I guess they never did because they were indeed bad. So I replace the mounts and while i had the mount under the battery out i decided now would be a good time to replace the speedometer cable due to a jumpy speedometer since I've had the car. So I change the mount, remove the speedometer cable, install new cable and test drive around the block. Everything seems ok. The next day I'm driving to work and the car suddenly goes out of gear at about 20 mph. So I pull to the side of the road and I have nothing, no reverse no drive. I turn the car off and start it back up and now i have drive again. I turn around and head home to get the truck so I can go to work. The car keeps going out of gear every 200 yards or so and I have to shut it off and restart it to get it back into gear. so I limp home and park it. The next day I'm checking for causes. The cable is the first thing I think of because I just messed with it. I pull on the back of the speedometer cable as it passes through the firewall to the speedometer and the cable comes right out, no resistance. I thought maybe that was the issue, the cable wasn't snapped into the speedometer correctly. I check the end that goes into the speed sensor and it also pulls free without releasing the clip. So, I take. the old cable and reinstall it since it worked besides the bouncing . Drive the car for about 2 miles and the same thing happens with the car going out of gear. I noticed while I was driving the speedometer would go to 0 when I would remove my foot from the accelerator. I limp back home and check the cable. The cable is connected fine to the speedometer but once again pulls free from the speed sensor. My question is, do I have a trans issue or is this related to the cable and speed sensor?