I too thought after winning a Slam, he would be able to relax and enjoy his tennis more. However, he still seems uptight and prone to taking the 'try not to lose' mentality on to the court.
I'm thinking it's time to accept that Murray will never be able to consistently play attacking, positive tennis like Federer and Djokovic have done. I know lots of people would say he's just not as talented as these guys, but personally, i think he's not far off, it's just that he's mentally too negative and nervous in the big matches.
Who knows, a holiday and some time with Lendl and his sports psychologist might be able to help in the off season.