1990 GMC suburban speedometer not working

[jesdude7789]

I bought a 1990 suburban a couple months ago and the speedometer was working when I got it but it has already gone south on me. When I am driving, it sometimes jumps to 65mph and stays still no matter how fast i'm going and then it well peg all the way up to the max sometimes and then back to 65 and then back to zero (or any combination of that). SOMETIMES it does work correctly but probably for only about 10% of the time that I am driving it and then it will mess up again. It's very random. I already checked the wiring on the sensor in the transmission tailshaft and everything looks good and went ahead and cleaned the contacts anyway and put it back together. PLUS, the odometer keeps working anyway so I'm thinking that the speedo needle motor itself is the problem. Anybody had this problem and found a definite solution?? I have read many other threads on this issue but haven't found any where the OP fixed it and lets you know how...
Is there a component on the circuit board the speedo is attached to that I can check with a multimeter and replace if it's bad?