The moment of truth in the golf swing is when the club impacts the ball and using an impact bag will help you get the correct feeling of impact
A tension filled grip, especially from having the shaft too much in your palms, will kill your entire swing. It stops your wrists from hinging naturally and then works its way up your arms and into your shoulders and locks up your entire swing.
Making mini swings with your elbows glued to your body will give you the correct sensation of the large torso muscles swinging the club, not the arms