Speed sensor ques.

Did you look at it already? Most 2005's would have a push in sensor held in by 1 bolt, it can be difficult sometimes to get the old sensor out, but once you do, it's just a matter of cleaning up the hole really good and pushing a new one in. A little grease on the new one helps. Just make sure it pushes in with hand pressure, do not try to force it in or push it in with the bolt, you will break it.

If it is a screw in one, do just like swaan said.

Also make sure that the trans yoke is tight, a loose yoke can let the tone ring spin and mess up the speedo. Loose yokes and wiring issues are more common than failed sensors, but it could be any of the 3.