I've been reading alot and decided to post. You guys are diehards. I am a diehard atv guy who posts alot on the atv sites.. Anyway I have a 98 F150 SC 5.4 auto w/ 285's, 355 gears. I just bought a 23' 98 Weekend Warrior. It weighs 4700 dry. I met a guy in Vegas. I live in SLC and he in Socal. I got a whopping 5.7 from Vegas to St George, Ut. It's all uphill and I did hit a headwind in the Virgin River Gorge. I got a best of 7.9. after I followed a couple of rigs for a while. I did 70 most of the way. I didn't even have quads or water in the WW.. I haven't done a tune up in a while 25k at least. Any good recomends for basic plugs wires ect. And i was reading the sponsers site. How much for the 1715 custom chip kit? I seen the 1715, but not the custom. DId I misss something?? Can I bring my truck in for the bulletins from Ford?? I bought it used 3 yrs ago?? Oh I have airbags on my truck and they work great. Got those, because I put an atv rack in my hitch and haul a 400lb quad on the rack which was sagging my truck. All has been well since the airbags..

 

Well, you are hauling quite a bit (at least 5000#), and then to go uphill with a headwind... I think you'll gain 10-15% in mileage just by driving 60 instead of 70.

 

ferroequine hit the nail on the head with the speed it plays a big role. Even still that does seem a little low. Are the tires a little larger than stock? That will play into it also. I think the 285's are larger than what came stock and this will affect your odometer which in turn will affect your mpg figures. You actually go farther than your odometer shows with a larger tire. Plus I found running a larger tire brings down your milage also because it takes more juice to spin a larger tire, ie. more weight.

 

Doesn't seem quite right sandstorm. I'd keep looking for a cause and get everything up to snuff as best as you can before you start upgrading. But then definately mod it as you canafford!
My truck is newer than yours, but same eng. and gears. I have an intake mod and the 1715 tuner, and they help, but not 4 mpg worth. My stock tires are 265s. When I pull my 24' travel trailer (5500# loaded) cruising 60 with OD off I get 10 mph. Less on hills I'm sure, but still enough higher than your's to suspect things. Did it seem like it was working too hard? How many miles on your truck? If you put the stock size tires on and you get 8 mpg on a level highway with a high milage truck, that may be the best you can expect. Just my .02.
As a side note, my old truck was a '90 F250 Scab 4x2 with a 460 and410 gears. When I towed my TT I got 7 mpg.
But I could go 70 up the mountains with it. Good Luck, Carl

 

Well my tires make the speedo off by 10%. I use exit ramps on full tanks to determine real miles and then what my speedo says on a full tank, 300 miles or so.. I always add in 10% to what the speedo says and that's how I come up w/ my numbers. Stock tires are 255 so they are alot smaller. I was hoping for 10mpg.. I have 58k on the speedo.. My 7.9 mpg was going over three 6500 ft pass's on I-15 from St George to SLC following rigs most of the way.. My truck worked hard on certain hills. I was a bit of a leadfoot as time is important to me.. I thought it would do better. I can harldy wait till the quads get inside for my trips to Glamis, Oregon and Idaho dune trips..

 

How much can the 98 f-150's pull anyway? You have the first generation 5.4 and that was the lowest for hp/tq ratings. The 5.4's from that generation had 235 hp and 330 lb tq. Don't quote me on those numbers. The 99 5.4's had 260 hp and 350 lb tq. You should also consider your axle ratio and tire size. Your mpg don't seem that far off considering your conditons.
Your like me, just can't wait to get riding. I can see my gas mileage drop when my foot drops also. Keep your speeds down and you will see an increase of 1-2 mpg.

 

Things to consider, Going uphill, headwind, Wow that truck was working hard.
Sandstorm, were you in OD ? or out ? What was your tach ? Seems a little low, but, like the prev. post stated you might not have as much HP as the newer trucks. All these things we're talking about are negative things working agaisnt you during the trip. I usually get 19.5 on the Hwy not pulling anything with an 03 Expy. I pulled an emty 6x15, V-nose cargo trailer (it's very lite) from SC to La. against a stiff headwind. I got 10 mpg, with my 03 Expy, 5.4, 3.73. I was horrified. On the return trip with a 83 magna inside (685 lbs), no headwind, got 12.5 mpg.
On the same Espy, pulled our 27' camper (7300lbs loaded) and got 9.6. Return trip with headwind, 7.8 mpg.
I havent pulled our camper any long trips yet with the lariat. Your mileage doesnt sound to bad considering the trip you took. If you keep the speed at 65 mph, you'll do better. You need to run down the hills faster to keep momentum going up the other side. People who pull heavy campers get pretty good at this. Dont floor it to get going faster. You cant do anything about the wind, man it's a real drag, like a huge boat anchor.