I still use K&N filters on my carbed stuff. I have one on my 4 wheeler. It has the outer wrap & the oil filter. I did not get any gains using a CAI on my efi motors. I wouldn't use one on my diesel because I want to keep as much dust out of my turbo as possible. The factory filter does a great job
I havent gotten a CAI for my V10 yet but I did put one on my 99 Mustang with a 3.8l V-6. Last summer I drove from WY to WA through MT and ID. The best mileage I got the entire trip was just under 27 mpg. Something like 26.7. When I got back home I had the exhaust dualed. True dual. No X or H pipe. Then I added a cheap CAI. I drove to Missoula MT, pretty much the same trip I had done a few months before. Used a stock tune and I was able to drive 347 miles on just under 11 gallons. Thats just under 32mpg. Only diff was exhaust and intake and I gained 5mpg. That was at 75 mph and 87 octane. Im really not not sure on larger pickups but on my car it was well worth it all to me.