https://www.youtube.com/watch?v=A2vD3mMrZbY
Sierra had the 6.2L which is the most powerful of the group (possibly also the fastest) and also rated at the worst EPA fuel economy. Not surprisingly to me, it won the fuel economy towing comparison.
GMC: 9.8 mpg
Ram w/ eTorque Hemi: 9.2 mpg
F150 w/ EcoBoost: 8.7 mpg
That puts the GMC 6.5% ahead of the Ram and 12.6% ahead of the F150.
I need the diesel to drop so they can test that trio since Ford and Ram have their 1/2 ton diesels already.