When you floor it in an automatic, the transmission automatically downshifts to a lower gear. That's why you feel the power come on.
When you floor it in a manual, you're still in the same gear that you were just in. If you want the car to downshift, you have to actually do it yourself. Hence the term "manual" because it's manually activated.
So in other words, there's nothing wrong with your car. You just need to learn how to drive the manual transmission. You'll get the hang of it and get it figured out in no time