Slowing down is not the answer. Quick tempo equals faster club head speed, faster club head speed equals longer distance, longer distance equals competative advantage. I was a 30+ handicapp and decided to go take some lessons. The first thing my swing coach did (who is the assistant golf coach at Cal Berkley) was put a David Leadbetter Swing Setter in my hand
Leadbetter Online :: Official Website of the World's Leading Golf Instructor and increased my tempo. Increasing my tempo meant hitting my 5 iron 200 yards rather than hitting it 160.
Your tempo isn't causing you to not hit the ball well, it's the other moving parts. You always hear people say to have a nice relaxed easy swing, sure that's fine, but you still need to generate club head speed to hit the ball 300 yards. It's about swinging faster, not harder.
I swear by the Swing Setter and highly recomend it.