About a month ago I bought the K&N FIPK and I have put about 1000 miles on it. Part of the reason why I bought it was because I scrapped the original intake system and I wouldn't have passed inspection in july so it was a good excuse I thought. The price was a not so modest $270 which I thought was pretty steep, but the cheaper kits were just that, cheap looking. Anyone who has looked into buying one of these already knows the price.
Installation was pretty straight forward except that it was 110 degrees in my garage. Follow the directions and you're done. Putting the weather stripping that seals the air box was a PITA though
As far as performance increase goes, I couldn't feel and "seat of the pants performance" but thats partly because my truck has a standard tranny and takes off a little bit better anyway. I did notice better acceleration between 2500 and 4000 rpms though. I also noticed it added a few mph between shifting, for example before the install I would shift from 1st gear to 2nd at 4000rpm, going about 30mph, after the install I shift at 4000rpm going about 34 mph. The biggest gain I saw was in 3rd gear (1:1 ratio). Previously I'd shift at 4000rpm going about 90mph, now I shift at 4000rpm going about 96-97mph. Ofcourse its hard to test that given that its way over the speed limit
Gas mileage gain wasn't that great, but I have a heavy foot so its hard for me to have good results, but there was a gain. Before the FIPK I was getting 11.27 mpg, after the install it averaged out to 12.70 mpg. So thats a good 1 1/2 mpg increase. Regular octane fuel was used. Now that I think about it not too bad actually.
So there you have it. I'll attach some pics.