I've been involved in striking arts for 4 or 5 years, mma for about a year solid and off and on for a few months before that. And currently I'm getting ready for my first fight. So I'm no expert but I know a few things.
First off, if you're doing really well on the mitts, decrease how much of that you do and spar more.
Another thing is isolation sparring. For example limit yourself to just your hands, and your opponent to lead hand/lead foot or vice versa, or hands only for both, or whatever, but limit yourself and your opponent so you can work specific tools in a live environment. That has done amazing things for my striking. Another big thing is intensity. All too often guys spend all their sparring time treating it like a fight, going 100%, beating each other with one guy usually dominating. You get jack out of that. You need to spar a lot with guys who can go 50%, just hitting hard enough that you get the message but not so hard that you cover and back away or turn away. And not so hard you get injured, or can't think. 85% of the time it should be calm enough that you can think about what you're doing and guys will back off once they've gotten you totally on the defense for a moment. I'm not talking about pulling things like in point fighting, or not being aggressive but just tapping with light force instead of really thumping each other, unless you're in camp for a fight there's no reason to do that much. When you're going "hard" in sparring it becomes a brawl usually and you get worse or you just can't work your game because the other guy is trying to beat you down. 50% most of the time is the way to go. You'll get better real fast. Hope that all helps.
Member of DaJoGen MMA school under Dave Hagen and Team Chaos fight team under Denver Mangiyatan and Chris Toquero, ran out of Zanshin Martial Arts in Salem Oregon: http://www.zanshinarts.org/Home.aspx