Can't figure it out....

[PewterPower]

OK....I have a 2003 H2 with 85000 miles. I have had no mechanical issues since day 1.

About 1K miles ago, I replaced the plugs with Bosch Platinum and according to the computer, my mileage dropped from 9.8 to 6.8......I asked this forum and learned that my Bosch purchase was poor and I removed and replaced the plugs with NGK....my mileage went back to normal range.

Next problem...I hooked up a 7x18 utility trailer with 4 ATVs (approx 3,000 lbs total) and pulled it from Tampa, FL to the Western NC mountains....my average mileage was 6.5.... I don't understand...I have made this same trip before with 8 ATVs and averaged 9.1 MPG....

Any ideas/suggestions on what my problem might be ? I have the Airraid replacement filter and it has been cleaned and oiled....the engine runs great...but I have no power...I had to put it into 4-Low to back the trailer up into the driveway.....

I need help and suggestions on what things to check.......Thanks !!!!

[Big Z]

when is the last time you had the tranny checked or serviced?

[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