2004 GMC ENVOY XL User Comment / Complaint

I have a 2004 gmc envoy (under 26,000 miles). i have noticed that after the suv runs for about 1/2 hr the speedometer will display my speed being below zero. in reality i am going about 50 mph. the speedometer is being acting very erratic. is there anything the gm can do for this problem. i am in the process of talking to the dealership where i purchased the vehicle. i have read about the similar problem to other envoy owners on the internet. i have also seen the same issue in other gm brands. i think gm should recall 2004 envoys for this problem.