I have 3:73s and like them. I get about 20 MPG or so and thats a mix of city/highway driving and of course a few 0-60 wot passes. I dont think you will see that much of a difference going with 3.42s from 3.23s, but i know 3.23 to 3.73 i saw a difference. I recently just did the same thing with my rear end after i demolished the posi unit