Power less higher in the rpms occassionally

Something's been happening with my car lately that I havn't felt like dealing with just yet, but I'm ready to tackle the problem I think. Sometimes the car will pull pretty high up just fine, but others it seems like the power just drops off at about 4,800 rpms. Fuel filter hasn't been replaced since I've owned it 6k miles ago, only tune up things that havn't been done is plugs and wires, so I'm wondering if any of those would solve the problem?

Car just recently rolled 90k, but I will admit when I first got it I'd gun it in 1st gear and pull it up to 6,200 before learning the limitations of the valve springs, and learning about valve float. As an update though, today the car's been running GREAT. I only bring it to 5,100 or 5,200 before shifting when I'm at WOT, and it pulls beautifully up to then and feels like it's got more in it. I'm planning on finishing up my tune-up soon, and also giving the MAF a decent cleaning although it shouldn't need it (can't hurt though!).