I have a 2004 FX4 screw w/5.4. I am interested in the possible benefits in mpg of using underdrive pulleys but know very little about them. I have read numerous articles and it's kinda like asking 50 people their opinion of global warming!
I have heard everything from 2 to 4 mpg gain, which I don't believe; to using underdrive pulleys will ruin your accessories, overheat your engine, so on and so forth.

I'd like to hear from some of you guys on here.

 

Tell us some more about your truck

What mods? Engine, gears, tires, etc;

 

My truck is stock. I have only K&N filter on it so far. 373 gear and factory exhaust. I am running on 285/70/18 Rugged Trail BFG's.

My plan is to run true duals, leveling kit, and Edge programmer. I was thinking about an electric fan conversion but not so sure about that now. My ultimate goal is to get the mpg up to 25, and I'm at 20 now.

 

Good luck reaching 25

What engine are you tuning?

Remove the k&n and use the factory filter instead or a dry filter, not an oiled one
Do the gotts mod if you haven't already

Get true duals:
94106 magnaflow high flow cats
X pipe
2 magnapacks
2 3.5/4" tips

Consider a gear change for your transmission and in town mileage, you'll sacrifice a little on the highway to lower gears

Do the electric fans and do some underdrive pulleys while your at it
If your considering edge, check out powerhungryperformance, it's a rebadged edge, black, and comes with better tunes along with the ability to custom tune to the mods on your truck

Better power, torque, mileage, quicker, firmer shifts, increased throttle response and shifting patterns are improved

 

He's got the 5.4. Not so sure about 20mpg in the 5.4...... How are you calculating your miles? Especially on 285/70/18's

 

20mpg is achievable on the highway

I get 18-21 at 75mph

From the factory she weighs in around 7500lbs

I now have 35s, and im 200lbs myself

 

my green truck gets 20+ with ease on the highway



OP do not get an edge, you'll regret it instead if you're hung up on that particular programmer check out the PHP gryphon CS with a mileage tune or the SCT livewire with a mileage tune