05' Rebel Feels Slow

For some context, this 2005 Rebel is my first bike and I've only had it for a handful of months. It might be because I'm just inexperienced, but I feel like its not going very quick for being in 4th or 5th gear. It sounds as if I'm really pushing it before changing gears and this is where I don't know if my inexperience is coming into play. Because I feel like its topping out at about 50mph while in 5th. Is it possible that I'm changing gears too prematurely, is that even a thing? Do I just need to give it some more gas? Should I just push it a bit more/longer while in each subsequent gear? I would love some input if someone has some.