It rides up my crack something awful

Ok while my truck is down I figured I might as well take care of some of its problems. One thing that is bugging me(but doesn't really har mme in any way) is that my speedometer doesn't work correctly.
Some of the symptoms:

It doesn't go to 0. It usually stops about 10-15 MPH
It usually won't start reading till I hit about 25 MPH or so
When I'm playing around and hitting excessive speeds when I let off the throttle and let the truck coast it hangs up at whatever speed I was going and won't read correctly until I get back on the throttle.

Also I'm not sure if it is related or not but the brake light on the dash is always on too. and no the E-brake is not on. I can't remeber if the ABS light is on or not.

I'm thinking it might be something in the PCM or maybe the speed sensor in the back axle or else the ABS system. Any clues? thanks.

 

Change the speed sensor in the rearend.