I recently purchased an 04 Chevy Avalanche z71 4wd, previous owner had a K&N fipk installed. I asked if he still had the stock air box and ducts and he looked at me funny but he still had it buried in his garage. I drove the truck for 3 weeks w the fipk and it felt sluggish on the low end. Today I installed the factory air intake w a new champion air filter and now the low end feels a ton better, more power. I did clean the MAF and throttle body since I had it exposed, wasn't too dirty. I would never recommend a K&N fipk unless you spend a lot of time in the high rev range but even then...