Previous thread is 4+ years old, and there's a lot more campers on Beyond now, as well as some newer trucks with better engines and transmission so I thought I'd ask. Also it's prime camping season, so more people probably have the info on hand.
Truck: 2011 Avalanche
Engine:5.3
Transmission: 6-Auto
Rear axle ratio: 3.42
Tire size: 265/65R18 (31.6")
weight of truck (including people and stuff in the bed): 6798 lbs (3090kg)
total weight of trailer: 5830 lbs (2650kg)
towing speed: 60-120 km/h
modifications: Intake, Headers, and a tune for the trip back
Mileage: Averaged 20.5L/100 kms for our round trip to Tofino and back. 677.7L used over 3302.5 kms.
I unfortunately didn't get the tune prior to leaving, and had it installed on the way back. It's actually a pretty shocking difference between the numbers though. Going from Calgary TO Abbotsford without the tune, so 3500' downhill, I got 23.9L/100 kms. Coming back Abbotsford to Calgary, so 3500' elevation gain, I got 21.5L/100 km