First and foremost, don't give up. Everyone goes through ups and downs in this game. There have been many times I thought about giving up, and I am so incredibly glad I never did.
The instructor may have a bigger picture that's hard for you to see. Have you asked him? "What is it you see in my swing? Where are we trying to go?" It's hard because sometimes it's a long journey and unless someone gives you a map, the trip may be frustrating. In other words, he may have specific reasons for everything he's doing with you, but he just might not have told him.
Or he may stink, it's hard to say. Talk to the guy and get a sense of what he's trying to do.
One thing is for sure, if you're 6'4, standard length and lie
clubs will definitely not work for you. You will have to learn to make corrections in your swing to make up for the short length and the too-flat lies. A lie that is too flat will only accentuate your slice: because of your height, the toe of the club is likely lower than the heel, which only helps you hit the ball right.
How long have you been playing? The more information you can provide, the more people can suggest things.
I think you can never read too much about the game. You CAN, however, get too many ideas in your head.
This book is, for my money, the best $10 I ever spent on my golf game:
http://www.amazon.com/Harvey-Penicks...e=UTF8&s=books
No matter what the condition of your game, this book will give you some fantastic insights into the game and the fundamentals of the swing. It's also easy to read, completely non-technical, and very enjoyable.
There's my 1.5 cents. More will follow from others I'm sure.