The Chevy 1/2 ton pickups,and SUV derivatives(tahoe,Suburban) tend to stay on the road a long time.Many, many of them make it well past 150,000 miles.It is true that the QC wasn't up to Honda/Toyota standards in the past, but they are much closer now.
18 mpg in mixed driving is very good.My Tundra V-8 accesscab(4400 lbs) never got better than 18 mpg hy(at 55mph),and only got 13.5 in pure city driving.It turned a lot or revs-2000 rpms-at 60 miles per hour.
I recently bought a 1998 2wd Suburban(5.7) with 196,000 miles on it.It came with full maintenance records which showed the trans was rebuilt at 185,000 miles(1st time),and the AC, intake manifold gasket and several other items were replaced at 165000.The seller didn't have any reason to conceal the maintenace record-it was selling so cheap $2950 no point.It has the usual 10 yo car rattles, but otherwise is pretty nice.It get 12 mpg in pure short trip(2 miles or less with full cool down in between)city driving with the ac blasting.My scanguage shows it getting 20 mpg at 55mph,and about 19 mpg at 60 miles per hour-not so bad for a 5400 lb brick.I expect that it will get 17-18 mpg on the same long trip route that the Pilot got 21 mpg on.In city driving the Pilot got 13-14 mpg.
Motor shutdown standing alone is a good thing.The V-8s use about .7gal per hour at idle(Pilot about .4 gal per hour).Most folks who spend 1 hour per day in city driving probably are stopped for 15 minutes of that hour-roughly .2 gal per day-65 gallons per year saved.
I'm pulling for GM.Their biggish vehicles-commercial pickups,SUVs-are what will make or break them in respect to USA manufacturing.
Charlie