I’m not OP and I’m sure he’ll have real world data. That said, My LT swap is just a pile of parts in my garage… and I’m in it more than $15k… I could buy a lot of fuel for what I’ve thrown at this project.Curious about this as well. Im thinking about picking up an 80 to do an LT swap with 37's. The two things I dislike most about my 100 are the power and gas mileage. If I could get the same or better MPG on larger tires with more power it would be a dream come true.
I wouldn’t make MPG improvement your guiding star. Even in an Escalade 4x4 with a stock tune and displacement on demand; the L86 was rated for 14 city and 23 highway. Add weight, 4.11’s, full time 4x4 plus the aerodynamics of a cobblestone and big tires, it can’t be great.