well i bought a 2000 suburban 4x4 with a 5.3 to tow my camaro and to drive every day. Well i drive 40 miles each way to work so i was a little worried about gas milage ...... so i have avg. out two tank fulls and im very impressed. this is with city driving and highway, on the high way i set the cruise control at 65 (our speed limit is 55) and with 87 octane and zero mods to the truck i have been avg. 17mpg.... i think thats great for a fully loaded heavy truck! oh yeah i checked RPO codes and its a GT5(4.10)....