ive got a 2004r behind a 355 for my daily driver, and i found me an auburn posi, and i was wondering if 3.08s would be better than 3.42s for mileage, or is there really no difference?

at the moment im not really striving for any take off capabilities, just gas mileage.. with the open rear with 3.42s (7 5/8) im getting 16 mpg, but some days i achieve 19, so what percentage would the 3.08s give?  

yes a 308 would be better for fuel mileage but you will loose some performance on low end but it wind more on top end.i have a 308 in my s10 with a 350 and i get anywhere from 19 to 25 mpg and i am very happy with it.  

wow, 19 -25 thats pretty decent, though thats a pretty light truck as well. thanks for the advice, i think im going to try out the 3.08s, its an 84 regal, i should gain at least 2 mpg.

thanks  

Yeah, you'll see a good economy jump with the 3.08 gear.

But make sure the stall of your torque converter will work with the 3.08 gear.  

i got the tranny out of a olds 307 wagon, i think the stall is 1800, the governor max is 3000 rpm, cause when im at wot my tach is pinned on 3000, kind of annoying   take off is awful, which is one reason for the down grade from the lower gear.

is 1800 stall good for 3.08s?  

the 3.08 would give you better fuel mileage. By how much, i don't know? good luck  

i installed them today after work, so far they seem to be forgiving.. im running 1700 rpm at 60mph w/o lockup, i havent done a wot test, or mpg yet hopefully both will make me happy.