slow internet connection when connect my macbook pro to the apple led cinema display

When I use my macbook pro to see videos in youtube or cnet the videos run very fast, but when I connect my macbook with the apple led cinema display 27" the videos run really slow. I always use wifi with my macbook without the display and run run fast. I also tried using the ethernet cable with the cinema display but still the same "slow". When I change the resolution of the cinema display runs better but I sacrifice the resolution and I want to use the display on the optimal resolution thats why I buy this display. I hope someone help me with this. Thanks.