My 2003 gmc slt Yukon won’t reverse but drives forward but isn’t switching gears

What is your question?

When in reverse doesn’t move sounds as if in neutral and stepping on the gas. When driving in forward position,it drives but doesn’t switch gears when reaching higher speeds. Is my transmission going out?

How long has your 2003 GMC Yukon had this problem?

A week but stop driving it when it wouldn’t go in reverse.