My E-150 is a conversion van. This is the 3rd E-150 I've owned since 1987. All feature the 4.9 liter in-line six cylinder engine. Put in a K & N performance air filter and she will run better on long steep hills. Expect 16 mpg which is about right for a heavy commercial vehicle like this. The tranny will fail at about 140K miles but used ones are easily found that can be installed for less than $700. I've NEVER worn out a Ford 4.9 liter engine. They still run strong at the 200K mile mark! But I add a pint of RESTORE at every oil change. Speaking of oil, I like Valvoline 10W- 30 best.
It has a 302 in it so it's very good on gas. I've had it for 14 yrs and only had to replace the brakes and belts. The normal stuff. I keep up on the oil changes. It only has 98,000 miles on it now and is very dependable. Starts up every time. It's great!