Did the same swap on my truck at the end of this summer. 4:10s to 3:55s on a 35" tire. One of the best things that i have done. It's like having an extra gear.
Mpg stayed about the same. 12-14 range. That's with an e4od, 238/100s, intake, exhaust, swamps idm and ts. Not tuned for the injectors...