"Stuttering" around 6k....?

[Addict]

For some reason my car has started "stuttering" at about 6k on up. By that I mean it sounds like the fuel is getting cut off or maybe the clutch is slipping. Its wierd because its fine up until 6,000 RPMs. As soon as it hits that it starts. Sometimes it acts perfectly ok. I'm not getting any CELs either.

Here's my list of engine related mods:
AEM Cold Air Intake
MSD 6AL Ignition (8k Limiter)
MSD Blaster 3 Coil
MSD Pro-Cap Distributor Cap
NGK Spark Plug Wires

I have 51,000 miles on her. As far as I know the fuel filter hasn't been replaced (at least not by me anyhow; though I don't know what mileage it should be done at; too lazy to go get my book). The plugs were replaced about 6-8000 miles back. I haven't pulled them yet to look at them. Any thoughts?