Speedometer's acting up

When I got my '90 suburban the speedo was stuck on 0. I drove it 1500 miles home to NY from Texas. It would stop at 67 for a while then jump back and forth. I believe at the moment it's stuck at full speed. Do I need a new one or what?

I doubt it's the speedometer itself, typically it works or it doesn't as it just displays the signal it gets whether its from a cable or a speed sensor. I don't know which 90's have but once you figure out what you've got then you can begin your search there. On my older chevys with speedometer cables they display the erratic needle swings just before the speedometer cable breaks but I've not had one "stick" on anything but zero.