I think my biggest problem is just a lack of fun items. There isn't really a reason to substitute out an optimal piece of gear of whatever build you're running with.
Sure, you are pretty lucky if you do have those end game pieces, but then what? Grind for paragon points? I don't enjoy rifts enough to keep running rifts for the sake of it. Hopefully with the next patch, things change a little as bounties can be a nice change of pace sometimes.
http://us.battle.net/d3/en/profile/Aeglos7-1318/hero/41640549
This is the one I use for solo play. For group play, I swap out Andariel's for Tal's helm, Cindercoat for Tal's chest, and Unity for RRoG. Leaves me with about 12.3m toughness and allows me to tank virtually anything in T5. I haven't found a T6 group yet.
Lightning procs with TF, Frost procs with Cold Snap, Fire procs with everything, and Arcane procs with Black Hole. Probably the most fun I have with group play.