Yes, I would say your rear sprocket is not centered on the hub. An off-centered sprocket will definitely make the tension go from loose to tight. Also, are you using thestock tensioner? If so, you might want to replace it with one of these:
Mounts to the engine and is easy on the chain. You can get them right here. Contact Turbobuick1 here on the forum. Only $40. One of the best purchases you'll ever make.