2004 Chevy Tahoe speed o metor does not work

You need to take it to a Chevy dealership and tell them that you want it replaced. There is a defect with the gauge cluster and GM has already sued the gauge manufacture over the issue. They have a certain mileage that is a cut off for them. I think its 75k. Tell them that you want it replaced at no cost. It falls under a good faith doctorine or something like that.
Really push the issue that you dont want to pay for it. Some of them may try to jerk you around but stand your ground. Then again they may order it and tell you when to bring it to them.