16 Sounds really low, especially if its being highway driven. Depending on the stretch of highway I get roughly 20.5 to 22 (while doing the math when filling up) with my Envoy and I have two extra cylinders haha. My city mileage falls in between 13ish, my previous TB Ext with the 5.3 was able to get 15-16 in the city thanks to DoD. I always had bad city MPG, no matter what my driving style was. My first Envoy was capable of getting 23.7 on the highway, but I was lucky to hit 12 on a good day in the city (I averaged 10 normally). Could it have been my driving style? maybe, but I try to lay off the throttle and let it coast when stuck in traffic. Highway wise, I always stick to 65 since that seems to be the sweet spot.