Did a tune-up today on my 03 Quadcab 4.7L with 103,000 miles. First thing I did was seafoam by using the vacuum line, some in oil and the rest in the gas tank. Followed directions, smoke, drove it about 10 miles then changed the plugs. Was original plugs and went with ngk iridium 6441's and put in a k&n air filter. Changed the oil from penzoil 10w30 to mobil 5w30 (not synthetic) and am using a fram hp-1 filter. Also changed the pcv valve. Took the truck for a test drive and after a few miles it sounded like a gust of air under the hood and a slight stagger in performance then normal( a little noise like the fan was loose or something just after the air noise). Drove it another short distance and the same thing. Also on my overhead mileage guage it has dropped from normally about 14-15 mpg to 8-10. What has happened? Anyone else ever experience something like this?