I bought the Envoy as the most powerful 6 cylendar for towing. I turns out I get better milage with an 8 cylendar truck. The air shocks were constantly pumping up, the fans for the climate control extremely loud, there is no vent setting so it was either blowing hot or cold air, wind noise was excessive, the gas tank is configured such that it always spilled over when filling no matter what gas station I went to. Passing gear was great but taking of from stopped was very slow for a 280 hp engine.
6200 lbs towing was great for a 6 banger mid sized SUV. That was offset by only getting 15 MPG. I get nearly 20 in my Dodge Ram.
Use quiet fans on the climate control and add a pass through vent feature. Gas milage must be improved. Ditch the air suspension in the back, it is just one more thing to break. Impove door seals for wind noise reduction. Change the rear gear ratio so there is some excelleration.