Pre/Post Workouts from GNC (packets) question

Well I broke down and decided to go buy some pre/post workout stuff in order to jumpstart myself again. I decided to give these packets a try again, previously used them shortly when I started lifting for the first time. Anyways, I noticed they seem to give me a huge boost with my workout. I can easily see it in my cardio but also in my general weight lifting routine, and was wondering what is causing this. I have taken preworkouts like jack3d and PRE but they havent done anything close to this for a long time. Any ideas whats goin on?

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