Can't figure it out....

[IRA51]

change the fuel filter and decarbonise the engine with GM top engine cleaner,and clean the throttle body . if you are useing an oiled air filter than clean your mass flow sensor with electrical parts cleaner . also if you went to a location 2000 feet in elevation above where you normaly operate the truck and you felt a loss of power than check your baro ,if it's out to lunch than you will loose power. also check your spark plug wires to make sure you didnt bugger them up when you changed plugs. if you have carbon build up than you will have detonation and the knock sensor will make the computer retard your timeing untill the it stops pinging thus reduceing power and fuel mileage . the computer will restore full timeing each time you fill up with fuel ,and than retard the timeing again if it detects pinging . I also sugest running a can of SEAFOAM in the gas tank to clean the injectors every 10 tanks or so .you can get Seafoam at Napa. good luck