89 suburban cruise control problem

[old man jimmy]

anyone found the answer to this problem with cruise? Works fine cold for a few miles, then kicks off. Colder it is longer it stays on. And when it's starting to warm up, will work uphill but when it lets up downhill, it won't kick in again. Sometimes you can push the pedal down & will catch. Have replaced cruise control modual, and turn signal lever(with the switches) still the same thing. Must have a speed sensor of sorts somewhere, but don't know where or what it even looks like. Speedo cable goes from speedo to trans one piece.