Re: comparing 4.6 to 5.4 litres
My wife had a 2003 with the 4.6, and she probably got about 14 mpg. She now has a 2005 with the 5.4, and we recently got 17 mpg on a trip. The 5.4 has a lot more accelleration than the 4.6, and has apparently been re-worked by Ford to be more fuel-efficient. Another thing different between these vehicles is that the 4.6 had 355 rear-end, and the 5.4 has 373 rear-end. The 373 should make the thing less fuel efficient according to the books, but it definately explains the increased pickup (in combination with the larger motor). So, in a nutshell, the motors are a bit more fuel efficient than before, but since when did Ford ever sell a vehicle because of fuel economy? They're valved differently, and thus have more low-end torque, but this comes at a cost of less MPG. Life is short: get what you want!