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I'm probably not going to be able to answer your question, but I would say that with no more detail than you've given it will be unlikely that anyone will.
I hope I can explain my issue with my 1995 corvette the digital display will freeze at any speed for a few minutes and then show the correct speed. It will also take a few minutes to show the display when I start the car.
Check the wired connection to the VSS, if that's good maybe the VSS would be next and likely a fix. The reluctor ring I wouldn't think could be your issue. I have a correct Kent-Moore Removal tool for that VSS if an autoparts store doesn't lend or rent. J38417 - 12$ and you pay the USPS and it can be yours.
Probably not the VSS. I can say this because I just finished replacing mine and read just about everything on this sensor. When this sensor goes bad it stops sending pulses or the output goes too low and then the speedometer will go down to zero. Shortly afterwards the malfunction triggers a fault code 24 and lights up the "Service Engine Soon" light on the annunciator panel.
If the speedometer is still displaying a reading and holding then suddenly changes to the correct speed display, it sounds like some computer issue. Like it is not updating the display for some reason.