This is on a 04 Santa Fe.

Here are the scenarios:

At speedometer speeds 0-80 The speedometer shows the speed correctly
At speedometer speeds 80-100 There is an offset by 1-2 clicks (so at 100, real speed is actually 98)
At speedometer speeds of 100-130, at actual speed of 120, my speedometer shows 130.

Anybody seen this issue? I though maybe tranny is slipping, but I'm not experiencing any other issues really(my RPM's seem to be fine), the SUV drives like a bat out of hell, but still this is a sign of concern for me. I'm driving it for a year now and the problem is not getting worse so I'm kind of deadlocked as to what the problem might be.
I was planning to go to a dealer with this but the last time I went I got ripped off, so preferably don't want to head that way.

Any healp, suggestion would be greatly appreciated.

Thanks