I just returned from trip to Florida where the trip computer reported MPG in the 7-8 range. I do drive near 70 MPH. I have the 5.7 liter Hemi and 3.90 rear end gears. RPM runs 2,000 when things are easy and runs in 5th gear(OD)and I will shift down to 4th (no OD) when going up a hill before losing too much speed and RPM will jump to 3,000-3,500. If you have a 5.3 liter engine and 3:55 gears you will spend more time in a lower gear raising the RPM and lowering gas mileage. My trailer weight is about the same as yours. The only cure if all that is true is to lower your speed so there is less air pushing on the front of the trailer. Good gas mileage and pulling a trailer are opposing goals.
