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 !!!!