I've noticed this year since I've been driving the car, at WOT in 3rd/4th gear and high RPM's (like above 4000) it feels like it's breaking up a little, like it's stumbling some. I realized I haven't replaced the fuel filter in awhile, I have a new one but haven't had a chance to replace it yet (have stuff for a new fence clogging up the garage atm). I know this could be partly it but it runs great at all other areas of the RPM range. When I had Lito revising my tune a few years ago he told me my car was running lean at high RPM's, even after he added fuel to the tune. He messed with it probably 3 times and told me it was still lean, but at that point I was pretty happy with the tune and it was running good so we never revised it beyond that. What would cause that, as well? Anyone else had that problem?