speed cal problem

ok
recently my speedo stopped working....so i replaced the speed sensor and it still didn't work so then i found there to be a bad wire from the sensor to the computer so i replaced part of the wire....and it worked for about 2 months then it would start bouncing when i hit bumps...so i checked for loose/corroded connections and didn't find anything
so i replaced the whole wire and now my speedo keeps maxing out past 150 and stays there.....
btw it causes my car to stall at stop signs.....unless i tap the throttle, then it idles fine
and for that 2 months that it worked the stalling went away..so i know it has something to do w. that
do you guys think that it could be my speedcal acting up???
its a dallas speed cal
thanks for any info