Drastic increase of gas mileage on my F 150

With all the gas milage stuff going on I decided I'd try to increase the milage on my 94 F 150 with the 300 cu inline six. Seventy Five thousand miles ago while driving from Home to Monterry Mexico I averaged 17 mpg driving 75 mph. The truck looked pretty nice back then with a 100,000 miles on the odometer (see picture with chromies on it). As of last week it was getting 12 mpg driving 65 mph.
I drive out to my son's place every day which is ten miles from my place which isn't very far but it adds up. So this week I lowered my speed to 45 mph. One of my rear tires was leaking air (has 4 or 5 plugs in it) I decided to change my tires from P235 R 70 15 to 35X12.50R15LT. The larger tire is about 8 inches taller.:whacked:
Now I'm sure some of you will question if the F 150 has enough guts to run them big tires, well it's got the 4 speed with overdrive and quite often with the stock tire size I would start out in 2nd gear, shift to 4th and then into overdrive.
I put the tires on and it drives great, looks a little funny (see picture), and low gear is low enough. Just driving along with the other traffic it looks like my speedometer is off about 5 to 8 mph.
Now I'll be driving at around 38 mph (which will actually be 45) AND I JUST GOTTA HAVE AN INCREASE IN MILEAGE.
I'll let everyone know exactly how much better it is.
My son said I was crazy but that now the lights shouldn't shine in any ones eyes.:LOL:

Just finished firing my '91 F150 6-in a row to break in the cam after a rebuild, so I will be very interested in hearing of any mileage increases with the larger tires. Good luck. :D

Well I had a big set-back on getting my "Drastic increase of gas milage on my F-150"; I've been hauling in scrap iron and my big tires started scrapping the wheel wells on the curvy roads, actually only the drivers side:CRY: I got back to my son place and changed back to the stock size (Picture of truck in front of my house). Total weight on trailer and F-150 was 3900 lbs, got $282.00

Other findings with the big tires: Tested speed with me pacing my wife's car, her at 30 - I was doing 25, her at 55 - I was doing 46. I took it up to 55 mph and I'm sure I was doing 70.

First load of iron hauled weighed 3100 lbs and the big 300 cubic inch six had all kinds of power (175,000 miles on it), even drove in overdrive with tires scrapping on the curvy road.

Have I given up? No! Might just have to take the sledge hammer to the wheel wells for more room though.:whacked:

Why not just add a set of helper springs?

http://www.truckcomponentsonline.com...-_c_254-1.html

I all ready have helper springs, and the rubber cushions are tight against the axle when hauling that much scrap.

A set of overload coils should give you some added clearance. I had a set on the 72 F100 I had with tires similar to yours and a load of gravel would just even out the stance.