The Expy MAX is the same size and wheelbase as the Suburban, a regular Expy is shorter. The big issue with SUVs is that they run out of GVWR before they get near their tow rating. On the Expy MAX with 3.73 rear axle and tow package the GCWR is 15,300 with a 9k tow rating and a 5,800 lb curb weight. They don't say what the GVWR is, you have to look at the B pillar sticker for that....nonetheless those are some pretty good specs for an SUV.
You can see from the specs that you only realize the 9k tow capability with 500 lbs in the truck...every pound of passenger, cargo and tongue weight reduces that 1 for 1. But if the kids are small and manage cargo you should be able to stay within weights.
I'm in the skeptic camp when it comes to the V6 ecoboost, but folks that own them say they run circles around the 5.3 and 6.0 from GM and get better mileage in the process.