My '07's sticker reads as "city mpg 14, highway mpg 18".

On a road trip, fill-up to fill-up, running 65ish steady, I usually get 20-20.5 when math is done, Scan Gage II is usually reading about 1/2 mpg higher on mine. Keep it under 60, I do a bit better.

Live in a rural area, can't speak to city mpg.

 

After a dozen years, I can tell you that you do not want this truck in NYC traffic.

 

The '04 that I bought new in Jan '04 was a great truck. Loved the styling being a first year design. Truck had the defective ring and pinion gears that were changed in warranty at 10k miles. 3 window actuators and one rear power window were changed in warranty. No sparkplug problems in 100K miles and the OEM's were still in when I sold the truck after 7 yrs. Engine ran strong and the truck's body held up great...looked new after 7 yrs. Brake pads and shocks changed once...gas mileage ran 14 in town and 16 hwy even with heavy 10 ply tires.

 

Yup, my '08 had the same MPG range on the sticker, and I average about 15-16mpg depending on time of year and fuel blend (e10 vs pure gas). I have the 3.55LS rear gears, and have seen over 18mpg on a long trip where the CC was set on 60mph, but I rarely ever run that slow. I'm usually running 70-75mph, so the fuel mileage takes a pretty big hit.

 

I bought my 2004 used last summer and now I'm replacing almost everything from the timing chain kit, oil pump, timing chain cover, VCT, etc... It really depends on the previous owner(s) and how well they've kept it maintained in the past. Do your research first and expect to drop a few thousand more for repairs if you plan on bringing it into the shop.

 

Every time a spark plug fires, the intense heat of the spark disintegrates a teeny tiny bit of the electrode. Over time, this means that you are removing material from the electrodes and the gap/distance between the electrodes gets slightly bigger and bigger and bigger. The bigger gap distance means that the spark has a longer distance to jump and that means that the coil has to work harder to generate the power required to make the spark jump the distance. Over time, you will put more stress on the coils and the coils themselves will fail.

On most vehicles its a lot cheaper to replace spark plugs than coils when they fail.

I have changed my plugs four times now, each at 60K miles. Have 220K on my 2004 F150 5.4L

Also since we are talking about plugs, if you have a coil fail, Replace with a OEM motorcraft coil that you can get on amazon for ~$45. Don't buy aftermarket coils especially the packs of 8 coils on ebay. They are all junk (Even the accel ones) and you will start losing them one by one over the next 20k miles. Ask me how i know. :-(

Also My truck has ticked (cam phaser ticks) since new. Sounds like a diesel at the drive thru. No driveability issues.

 

In my area a plug change on a '06 5.4 3 valve, at the dealer will cost you about $350.00 and require the truck to remain overnight at the dealer.

 

That's pretty fair for a dealer.