I think u need to have more patience (in general when u play chess)
Because the thing is, u are used to trying to attack as fast as possible, saccing, and mate. In closed positions, I think its the same thing, but u have more time to bring all ur pieces to best squares possible, and than break through by saccing, and than mate. Whenever u play, try to think how can i improve my position when it is closed, because u have the time to do whatever it is u need to accomplish in ur position.
I would continue to work on tactics for 15-30 min a day just to keep sharp. Also, I think Dvoretsky may be a bit over your head at the moment. However, I would recommend My system by Nimzovitch in order to gain a more fundamental understanding which it seems you wish to gain. Don't supress how you like to play but improving your weakest points will no doubt help you to improve!
Zach