You're not going to go up 5 pounds every week. This works for beginners but only to a point, and you're most likely past this point. In my opinion, going to failure on the last set of every exercise is way too damn much, and lowering the weight and working back up doesn't mean 10 pounds. Like austin said, you need to cycle your rep ranges. Working up to a heavy triple every time isn't going to work for long.