Ok,ok.
@Dala, get a propane torch. Heat just the plug. It will take a very long time to heat since aluminum disipates heat very quickly, and the trans oil will too. Dont worry, you will not melt the aluminum or cook the oil. Now while heating the plug, spray around the plug with penetrating oil. Take your pick, they all work well. When you spray the plug, the heat will suck the penetrant into the threads. Keep doing this, heat, spray, heat, spray... Finally, get a half inch impact, bare with me, it sounds crazy. What you want to do is after heat cycling it a bunch of times, get that fucker HOT. With the impact on reverse just bump it. Do not try to back it out. Just bump it.
Now, before you re-install it, put some anti-seize on it.
As for the speed sensor, get a pair of channel lock, the medium ones work the best, and a small pry bar. What you want to do it grip the sensor with the channel locks just under the connector. The sensor is fairly strong. While pulling up, twist the sensor. Every now and again put the pry bar under the channel locks and pry up on it. I would suggest you get a telescoping mirror so you can watch your progress.
Try it, dont try it, its up to you. I've been a diesel tech for 8 years now, and have picked up some tricks along the way.