Don't change the gears (cassette and chainrings) if you're going slow, probably only worthwhile if you're having problems climbing uphill or keeping up with your buddies downhill...

Have you been riding a drop bar road bike? In general they are fit to put your upper body in a more aggressive forward angle than the setup of most hybrids or mountain bikes. Maybe you're not used to that? You can flip the stem up to bring the handlebars up and closer before you go to a shorter stem. Good luck!