This could be a lot of different things. First, fill in your signature so we can see what year of truck you are talking about. Then tell us which gears shift OK and which one(s) hang up until you lift off. Tell us if it does it all the time, or if just sometimes, when does it happen.
For example, hanging 2-3 shifts and sometimes failure to go into reverse might be hardened and leaking seals in the transmission.