The 97 F150 4x4 I had with a 4.6 had 283,000 miles on the engine and 270,000 on everything else and still got around 23mpg.
The 5.4 is junk in my opinion, the 4.6 is a much better engine. The 4.6 transmission will bolt to the 5.0/302 but, you won't be able to bolt a starter on.