It sounds like, if anything, you're new tires are slightly less diameter than the 225's (too lazy to open calc.exe). So they're a little wider (potentially a little more friction) but a little less diameter (slightly easier to rotate) which should be a wash basically.
1.) How much less gas mileage? Have you calculated by hand, driving most of a tank?
2.) Did you change those other things the same time you put on tires?
3.) Is the truck throwing any codes? (Never hurts to ask
My truck is basically the same as yours. With my 225-70R14's and the 4.10 gears, I usually get about 25 mpg in the summer and 20-21 in the winter.