Originally Posted by chaseav
I drive a 2007 Chevy Avalanche (1500) 2wd with 5.3L and 3.73. I am a pilot so I am constantly monitoring anything that can be monitored and in this case, fuel burn and trans temp are about it. When I first got the AS back in Dec, I was shocked to see my truck go from a highway average of 20 mpg all the way down to more like 8.5 once hitched. This terrified me.!
Not a total surprise. I used to tow a 6,000 lb 27' Safari with a Chevy half ton van. 5.7 liters with a 3.73 axle. Tow vehicle was not rated to tow in OD so I towed in 3rd. Mileage was between 11-13 mpg at 60 mph. Considering I went to a 3/4 ton GMC van with a 6 liter gas 4.10 axle and now pull a 30' Classic slide that weighs about 8,600+ lbs (depending upon how much fresh water I pull). That vehicle does the same 11-13 mpg. I attribute that to the fact that the transmission on this van is rated to tow with OD (as long as it isn't hunting).
The big difference however is solo city driving. That half ton did about 17-18 mpg where my 3/4 ton is still 11-13 mpg. I pretty much attribute the betterment with the half ton is the axle and OD driving.