The 4.6L SOHC modular engine appeared in 1991 in the Lincoln TC and related Panther chassis cars. Aside from changes in manifolding, etc., the engine has remained the same throughout the years. I presume the engine is still in production, but I'm not too sure about that with the advent of the 5.4L Triton.
The 4.6L SOHC has a record of reliability, durability and economy largely demonstrated by its use in the Ford Crown Victoria P71 Police Units. Cars outfitted with the engine have been the favorites with New York taxi cab operators for the reasons of size, reliability and economy.
Members of the Lincolntowncar.org site (of which I am a member) have vehicles with more than 300K miles on the clocks, some even exceeding 400K with nothing more done to the cars other than regular maintenance.
My 1994 LTC (4.6L/AODE) has 160K miles on the clock, runs perfectly and gives around-town driving mileage in my area of 21.5mpg even using the cheap gasoline that contains 10% ethanol. Straight 87 octane gas would give 1-2mpg more mileage.
The car makes 30mpg at a steady 50mph in OD on a flat road, 24-26mpg at 70-75mph cruise and 17mpg at 95mph.
When I was looking for a truck I chose the F150XLT with the 4.6L/4R70W combination based upon my experience with the same setup in my LTC.