2003 GMC GMC TRUCK User Comment / Complaint

My 2003 gmc sierra 2500hd just started having speedometer problems. all of a sudden i was driving down a country road traveling about 45 mph but my speedometer said i was going 90 mph. then it all of a sudden went to 120 mph and eventually it pegged out completely. when i turn my engine off all of the other gages go off but the speedometer stays at 120 mph +. sometimes it fluctuates between 70 and 120 + but it is never correct. this seems like a huge safety issue and it appears from reading online that there are tons of other people out there with the same problem. this seems like something tha gmc should fix for free considering the safety issues. we dont have the money to spend on something that is obviously the manufacutrers fault.