There seems to be some narrative that he can't run because of his knee and I've heard Bisping saying; 'get a thread mill, buddeh, if you want to improve your cardio' I reckon it's a slight mental thing. He's not used to being in wars - aside from Diaz II and maybe against Mendes in the 2nd round. Aside from Diaz, I can't see anyone taking some of the shots he landed on him. And while the likes of Ferguson and Lee probably won't stand with Conor, they have to get in close to try and grab him down.
Like someone said a few posts above, he probably needs to conserve his energy better and perhaps learning to breathe better the longer a fight goes. Cruz talked about how he learned some technique from a triathlete. That's two fights where his tank went completely - one in his pro boxing debut, in a 12 rounder against someone who is 49-0 - the 1st Diaz fight and he did have a lull in the 2nd Diaz fight, but Diaz was also gassed in the 4th round.