I towed a lot with my 2010 and 2012 Acadia, bottom line... fuel consumption is absolutely terrible when towing.
The best way to reduce fuel consumption, lower engine coolant temperature, and to be happy with the power is to simply use gear setting L.
Around town use L3 (uses only 1st thru 3rd gears)
More country roads use L4
Flat freeway driving, use L5 and keep it at 60 mph or under
Feels like you are using more fuel because your RPM is higher, but it actually is using less because you are not under as much load with the engine running closer to peak HP range.
2008 SLE AWD 8psg Medium Brown Metallic RIP
2010 SLE2 AWD 8psg Summit White / Sunroof / tow pkg Traded-IN
2012 SLE2 AWD 8psg QuickSilver / Sunroof / Bose Traded-IN
2017 SLT1 AWD 7psg Summit White / Navigation / Sunroof / Bose / Tow pkg