Problems streaming iTunes movies to Apple TV

I can stream iTunes movies to my iPad, iPhone and MacBook Pro without any problems (usually), but for some reason getting to play on my Apple TV is hit or miss. They take a very long time to load, and most of the time I have to change the settings to standard definition to get them to start at all. I realize that my internet connection is probably partially to blame, but why is the Apple TV the only device that seems to have problems? I have tried unplugging it and resetting it. I would like to transition away from DVDs and Blu-Rays and start buying all of my future movies from iTunes, but until I can get this issue resolved, it doesn't seem to be a viable option.