2007 GMC Canyon Fuel Mileage

I own a 2007 GMC Canyon in-line 5 3.7 litre truck. She is 4X4 and runs like a charm. Only issue is with the fuel mileage. There are no CEL present. I get about 300 - 330 km per tank of fuel. 90% city driving. I've replaced coil packs, spark plugs, air filter and upstream O2 sensor. Doesn't make any difference to fuel economy.
I do run with max size rubber on her which is 265/75R15 or 31x10.5R15.
What else can I try to improve fuel economy???
Thanks for all input!