I cant comment on the 4-cyl Rangers but I have owned a pair of 3.0L with Automatics and extended cabs, both got me around 13 mpg on average. I gave the 2003 Edge (my first one) to my Granddaughter and then had an accident in the replacement Ranger a 2004 3.0 that totaled it. Both of them have/had well over 100000+ miles each with no major mechanical concerns.
I like Rangers, they suit me fine for my around-the-town driving so I looked for a 3rd one. Found a 2011 4.0L Extended Cab at a local Dealer with 44000 miles and bought it.
I was concerned that the 4.0 would give me terrible mileage and present problems but I have to say, other than normal maintenance there have been no additional repairs needed or performed. Best of all, I was surprised to see my mileage increase to 16+ mpg avaerage and I have a heavy foot.
Have to say, I wouldnt be afraid of a 4.0.