Got my 1974 F250 Camper Special done. Rebuilt the 360, installed rebuilt Carb.
2 barrel. Truck is original. Took it out on the highway after I put 500 miles on it, kept it at 55 MPH, accurate check 10.5 MPG. Plugs look great. What do I do when gas goes to $4.00, and it will ?
Dana 60 4:10 rear end like mine? Change it out to something like a 3:54:1 gear set (Summit Racing, others). I'd like to do this myself, but the pickup is used for hauling stuff and not as a daily driver, so I can't quite justify the cost to change it over. (And I'm not quite sure I'm capable of doing it myself without mucking it up). The axle change will help get 'better' mileage, but it won't compare to having a modern overdrive transmission.
From a post on this site in 2009:
"Look for a 67-72 F250 with a "37" axle code, it will be a 3.54 ratio which is approx 5% less RPM's than the "38" axle code 3.73 ratio, and approx 14% less RPM's than a "24" axle code 4.10 ratio. A "C7" axle code is even better, it is the same ratio and 5300# weight rating as a "37" but with a locking differential. A lower numerical ratio reduces RPM's. Less RPM's at cruising speed helps gas mileage and reduces engine wear but reduces acceleration and towing power. 3.54 is the numerically lowest gear ratio I have ever seen in a 67-72 F250. I have seen 3.07-geared Dana 61's used in F250 trucks, but those were 1977-79 trucks with 400's and automatics. Newer axles will be too wide to bolt into your '69 F250."
engine is still tight at 500 miles. as it breaks in more it should loosen up a bit and give you a lil extra but yeah, it is the nature of the beast so to say.
Rich
1973 f350 super c/s 460/c6 22k orig miles
1972 f350 srw crewcab special 390
1972 f250 4x4 sport custom 390fe Red
1972 f250 4x4 custom 360 FE " Ranger Ric"
1972 f250 4x4 custom 84k og miles 390
1971 f250 4x4 sport custom 56k og miles. 360
1970 f250 4x4 428 fe hp60 205 d60
Dont eat yellow snow.....
I have had a few of these trucks in my time. I DO NOT drive them for MPG
May your sails stay full, and your knots not slip. Unless a slip knot.
Once I thought I was wrong, but I was wrong.
Life is a banquet, and every days a feast.
68 F-250 CS 390 C-6 P/S A/C front disc. 2nd owner.
2016 GMC Terrain Denali 301 HP V-6 AWD.
2009 Silverado Crew Cab, V-8, 4X4.
DD-727
DD-806
AE-35
LSD-39
AS-41
AR-8
Well, I do have to come clean. I have an old camper box on it (no real weight) but it
does stick up vertically 22" higher than the cab, so a lot of wind pressure. Also, as
a plus, I inherited the truck (all original) with 62000 miles on it. Stored in a barn since 1982, it belonged to my father in law.Put $2500 into it. Now I have a truck that turns heads. With the price of new ones I can buy a lot of gas for $25000.00. Not tha depressed after all.
My dad had an early 70's with a 460 in it. He said it got 10 mpg uphill, downhill, engine on, engine off. He was right.
You want good mileage you need to look elsewhere.
1968 F100 SWB Flareside, 240-6, 3 speed, 3.70 rear, bone stock and rust free.
Got my 1974 F250 Camper Special done. Rebuilt the 360, installed rebuilt Carb.
. Here in germany we pay around $ 5,38 per 1 gallone 
. Six months ago, it was even more expensive...