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Currently have a 2014 Silverado Z71 2WD with 3.42 gears. I've done the RC 2.5" level and popped some 33's on it (really 32.6") and noticed a drop in mpg and towing mpg. The truck sees about 25K miles per year as it's my daily driver (mostly highway) and I'm towing a 5,000 boat package (including trailer and all) about 1-3 times/month. My question is, would upgrading to the Zone 6.5" system and 35's (really 34.8") necessitate upgrading my rear differential to say 4.10? Or am I safe to stick with my existing gears? Any experience with this setup? I'd like to avoid the cost of a gear swap but obviously want to stay practical and reliable. I'd like to get 200K miles out of the truck if I can help it.

 

Thanks!

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If you have a 5.3/6spd although not optimal the 3.42s will be ok

 

 

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I would swap, personally. I have 3.73 with 33s and feel like I'm at the limit to prevent crappy shifting/loss of power/loss gas mileage etc. See this chart just as as guide gear_ratio_chart1_zpsgmppgfyu.gif

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Thanks for the replies everyone! Keep the info coming. My only concern with that chart is that it's basically saying I need 4.10s with stock tires...not sure that makes much sense. But I could be looking at it wrong.

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Thanks for the replies everyone! Keep the info coming. My only concern with that chart is that it's basically saying I need 4.10s with stock tires...not sure that makes much sense. But I could be looking at it wrong.

that chart is for 4l60e transmissions

 

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There are plenty of folks in the Lift thread that say they have 3:42 and can chirp their tires still with 35's and its wasnt a problem

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I would swap, personally. I have 3.73 with 33s and feel like I'm at the limit to prevent crappy shifting/loss of power/loss gas mileage etc. See this chart just as as guide

I think the 3.73's are perfect for 35s, 3.42's will be just fine, some even have 35's on 3.08's and are satisfied.

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IMO - Ideal setup.. Plenty of power & mine would spin the tires with 35" MT.. I do have tuned, headers, exhaust, etc.. NO NEED TO CHANGE even with 37.5".. Up to you. :dunno:


IMO - Ideal setup.. Plenty of power & mine would spin the tires with 35" MT.. I do have tuned, headers, exhaust, etc.. NO NEED TO CHANGE even with 37.5".. Up to you. :dunno:

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I have 3.42 with 35s with black bear tune and they move!! I do have an avg mpg of 14 mix of city and highway. 15-16mpg on highway not towing on 91 octane. If mpg was a big concern for me i would go 4.10 but i have 4wd so thats double the cost to regear

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