speedo

Need help. 88 ck 1500 700 R4 254000 miles. Speedo bounces around. Replaced VSS, solder all connections on back of instrument cluster, and traced all wiring, no rubbing on pinches. Dont know whats left for sure?
This is a intermitte problem. I've been told that there is a vehicle speed buffer that converts the vss signal to a digtal signal but I can't locate anything like that. I guess it helps to know what and where you're looking for this thing. Please need help?

The buffer is straped to the top of your computer. Usually its under the dash on the passenger side. hope that helps.

If you take the glove box out, you should see it. Possibly a white plastic housing, about 3x3x1/2". has a wire harness going into it, and might have been velcroed to the dash to lessen vibration.