i dont know if this info will help at all...i have a 1997 c1500 with a
4l60e and a while back i unhooked the speedo wire from the speed sensor and it went into neutral as it shifted from 2nd.....i am for the most part a c1500 expert ive had it since it was new and have gone thru the whole thing top to bottom ....but if theres 1 thing i dont know its transmissions! everything else is a breeze ...