Cohesion
 

Is there any way to speed up cohesion increases aside from just playing people together?

There's an entry in training camp for it. Team Functions if I remember correctly.

Anything else? I already allocated 3 hours to them in TC...

Unless this has changed from the FOF2 days, cohesion is relative--so if yours increases while everyone else's does as well, then you won't see that increase reflected in your rating.

It's definitely relative. In the IFL, at the beginning of the second year when I started it was all 90+, but some have gone down. The IFL now has a bunch of people in the 90's who still ahve original players, but the mean is going down.

Do team leaders have an impact on cohesion?

This is a mystery to me. I have units that have been playing together for years, and yet their cohesion is still low. On the other hand, units I have chopped and changed often don't seem to suffer. There seems to be no logic to it.

If everything is relative as suggested, you may not be able to make much sense of it, without knowing each and every team inside and out.