Yes very much comparable in MPG and used prices, with the Sub having about about 20cu' more storage room behind the 3rd row than the Tahoe. Really makes a difference if you have more than 4 people/dogs to haul. Found the same relative difference in pricing when I was scouring the north half of L.A. county for mine last Fall. Tahoes were $500-1000 more. I also noticed that the GMC Yukon variants ran about ~$1200 less than the Chevy-branded versions, everything else being the same. I noticed the Yukon/XL ads seem to linger longer. Not sure if it was lesser demand or people just not considering them.
on a related tangent I found a similar trick a few years ago while planning a trip to Albuquerque for their Hot Air Balloon Festival. Hit all the travel sights for hotels in Albuquerque, everything all booked up. Looked at some maps and tried again plugging in their 'Rio Rancho' NW suburb and bam plenty of bookings available. So maybe searching for 'Yukon XL' instead of Suburban is the way to go.
I'm getting about 13.4mpg in my sub, the missus gets a hair over 14 in her Tahoe. But her commute is mostly highway driving and I'm a leadfoot with a lot of local driving. Switch vehicles and we'd likely get the same numbers or close to it. Same 5.3L/4L60E drivetrain in both. Hers is 3yrs newer but has 25k more miles on it.
The Sub will give you a full and flat 90", with the 2nd row stored. The Tahoe a tight 72". 2003-on the 2nd row headrests fold back / up when you drop the seatbacks, about a football-sized lump in your way on that 72". 2000-2003, the headrests pull out manually they fit in the tiny 3rd row footwell and are covered by a flap board on teh backs of the 2nd row when they are folded down.
the Sub