2002 Dodge Ram 4.7 liter 1500

:( I would like to know if it is normal for my 2002 ram to be getting only 10 to 12 mpg a tank! My fiance has a 02 model also base model with over 100K miles on hers and she is achieving 17 mpg on highway. I am saddened by this and am thinking of trading it I have barely had 2 mnths. A 4.7 liter should do better from my understanding. Also I notice hesitation and like the tranny is straining what gives. I put a K and N airfilter nadda nuttn! Any advice. Maybe put it on diagnostics ! Any help or advice I will take thank You !