The only stretch of Berkman's career that is somewhat comparable is early 2005 when he was coming back from his knee injury. He was slugging .346 on June 20, 2005 and finished the year with a .511.
I don't know what the problem is. Everyone has been waiting for him to turn it around for some time now. This is a guy who hit 45 fucking homers and drove in 136 fucking runs last year.