Loyalty to team. Team members support each other and defend the team from any outside attacks, both real or perceived. Team members also talk about the team and its members with pride. Lots of work starts getting done. This is how you can tell you've reached Stage 4.
Enthusiasm is high, tasks get accomplished, and visible progress is being made.
It takes time and effort. Reaching Stage 4 does not mean that all members like each other or are friends. What it does mean is that the individual members have worked through a number of issues and have concluded that the team's goal is worth accomplishing and that being on this team is the way to do it. The following is a checklist of sorts to help you have a successful team experience. Doing all the things on the list can't guarantee success, but not doing them will almost certainly ensure failure.