AXLE GEAR SWAP - real numbers
In case anyone is interested in the effects of changing the axle gears in your truck, here are some facts from my experience:
I like the 4.6 engine in my truck because of it's reliability and now, post gear change, reasonable mpgs for this type of vehicle. And, much as I love the diesel trucks on this forum, I prefer gas engines for myself.
Awhile back I replaced the 29" tall street tires with 31" tall GY Duratrac E-rated tires.
I just recently changed the gears in my truck from .355 to .410
These are most likely the contributing factors to what I consider less than satisfactory mpg's and also, on the highway at around 62mph, the engine was turning about 1450rpm. Obviously way too low to make power, so the autotrans down shifted on all but the slightest incline. Which for me, was extremely annoying. I installed an aftermarket exhaust which helped the mpg's a bit, then installed the gears.
After installing the gears, I calibrated the Edge monitor mph by using the tire size adjustment feature and comparing it to gps speed. It is calibrated to within 1 mph high. As you can see from the pic of my Edge screen, the gear change has resulted in about 500rpm increase. This has proved enough to allow maintaining highway speed without downshifting, short of climbing a proper hill.
Although the means by which I calculated distance (because the dash odo is no longer reliable with the tire/gear change) is slightly suspect for my math, a rough estimate is a mpg gain of about 1/2 to 1 mpg. Which raises my trucks efficiency, loaded, to a little over 15mpg's. When I have a chance, I'll use my other gps which I think will make it easier to calculate mpg more reliably. I'd consider anything over 15 to be reasonably efficient for a loaded overland travel vehicle.