every truck will vary and winter fuel can effect the mpg as well. Driving style, distance driven daily, stop and go traffic, wheels, lift and so on. The more miles you get on her the better it will get, but like I said, some trucks sip, some drink and some guzzle!
My LLY, 2004.5 I see 14.5 in town and on the freeway @ 70mph, my sweet spot, I can pull 18.6 to 19.4 (best) hand calculated.