Speedometer stopped...so did cruise

[retx]

I did a search and couldnt find specifics.
Yesterday my speedometer started the bouncing bit. From a stand still, starting off, it would immediately start bouncing from 0 to 25+, up and down, up and down. Then once i hit 25, it would settle down and read fine all the way up. When slowing down, same thing...fine until i reached 25 and it would bounce until i came to a complete stop.
1. did the speedometer die, or did the cable go? or something else.
2. why did the cruise stop working as well. Is the speed sensor for the cruise control amp connected to the cable in some way? or the speedo? or the transmission.
3. if the speedometer died, is it ok to put in a different mph one in? i have an 85mph speedometer.