After doing a tune-up on my 2.5L (mileage is 150,000) im getting 26 highway and 21 city. This is with an Automatic and 4.10 gears.
My tuneup was:
New spark plugs and wires (motorcraft plugs and BWD wires)
new air filter and fuel filter (wix)
new pcv valve (BWD)
cleaned out the whole intake manifold (lost of crud in there)