2004 nissan sentra spec-v ser 2.5l, 175hp, 6speed, 4cyl. factory mpg specs=23/29. so any way the 23 city would be roughly correct, but the 29 highway is a joke, you get that on a good day driving behind my grandma, its was more practiclal to say it was 24-25 mpg highway. I bought the professionals tornado fuel saver (as seen on tv) and it actualy worked, bumping my practical highway mpg upwards of 27-30, and yes i know alot of people dont believe in performance mods such as these, but it actually worked. I drive 34 miles to and from work. a guy i work next to lives in my neighborhood. In a conversation he said that he gains x amount on gas by driving 45mph in a 60/55mph zone, and this is why i couldnt ride with him due to the fact that i drive with the mentality that I will be the passer and not the passee, and i just hate riding with other people. So pondering the idea, im on my second tank of gas now, i decided to slow it down. speed limits are posted at 60mph half of the way and 55mph the other half. so going from always doing 5-10mph over, i set my cruise at 50mph and my rpms run 1900 the whole way. now hold on cause its realy unbelievable, i now get 38.1mpg on the highway. i did try the 45mph but the rev's were too low to pull some of the hills eficentialy. so 50 it is. So anyway thats my story and im sticking to it .