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When you state it moved up and down, you mean it bounced? Does it do it at only certain speeds or at all speeds?
The most common on this issue is a bad VSS. It is mounted on the transmission just before the output shaft. It detects your road speed. When it messes up, it will make the speedometer bounce or drop out completely. Change it out first since they are very difficult to test and are pretty cheap. Then see if the issue resolves itself.
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