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CJM8515 said:
Debating 4.10 or 4.56 for my 12 Sierra 5.3L, 6L90E, diablo 87 tune (mostly cause super is $$$) and 285's. Stock is 3.42, 3.73 would bring it back to stock, and 4.10 would be a jump above. I dont tow much and dont plan on it anytime soon, I commute quite a bit on the hwy 70-80mph for a good 80 miles round trip 5 days a week.

My mpg is pitiful, currently getting bout 14.5-15mpg highway, although AFM is off. Seems the engine lugs to much imho, I need to get it to downshift maybe 1-2 gears to pass someone.

Im thinking 4.10 would be best overall and might give me better mpg as the engine wont lug to much? 4.56 might be bit much IDK.

Found this site that sorta explains what rpm Id be at with each setup and tire size: ... o-1500.php're thinking is backwards. you dont get better gas mileage normally going from 3.42 to 4.10 or 4.56.

I wouldnt do 4.56 unless you're on 37s or bigger or if you tow heavy weight. (6k+)

If you really needed 4.56... then i think you need a 2500 first.

I had a 2011 1500 5.3 with 3.08 gears (6spd).... UGH. moved to a 2004 2500HD with 4.10 (4spd OD).... and good gawwwh its so much nicer.
i dont even have a need to go to 4.56.
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