Some people report getting better vapor production by removing one of the top wicks from the coil, (I'm assuming you're using a Kanger coil) have you unscrewed the coil, pulled the center post out of the coil and looked at the coil itself? It could be that your juice is one that rapidly gunks up the coil, affecting your vape production. I don't know if that could have anything to do with overheating though, there are a lot of people here with tons more knowledge than me, hopefully someone with this problem will have a solution.