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I just bought my new RAM. A Sublime Sport crew 4x4 with the tow package and I was wondering if there's a difference of mpg between the 3.92 and the 3.21 gear ratio?
 

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I have been reading thru most of the old threads here about 3.21 vs 3.92 (with 8 speed trans). I can see having the 3.92 if you really are doing alot of heavy towing.

I have decided to buy a truck with the 3.21. Ironically I have only found a few trucks so far that were what I am looking for, except they have 3.92.

edit: After reading what I posted above, just to be more clear, what I meant to say was I have not actually bought a truck yet, but when I do I plan on it having the 3.21. I have passed on a couple already that I have found that would have been a good deal, but they had 3.92. I might also be okay with the 3.55 especially with the V6. I would probably only consider the V6 though if it was a really really good price.
 

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I think a lot of it depends on the dealer. My first dealer that I bought my 2015 Ram from pretty much everything they had on the lot were 3.21 open diff. trucks and they had a bunch of trucks both 2 and 4 wheel drive. When I bought my 2017 back in April I decided to widen my search to find a better deal and ended up buying from a dealer than was in a little country town 100 miles away. He didn't have as many trucks by a long shot but damn near 90% of the trucks on the lot were 3.92's with limited slip. He only had a handful of 2 wheel drive trucks too. I ended up with one of the 3.92 trucks(obviously) and it is a bit more fun to drive with the lower gears but you definitely can tell the difference in mileage. Its a solid 1-1.5 less MPG with the 3.92's.
 

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I think a lot of it depends on the dealer.
I agree. The dealership that I have purchased both of my Ram trucks from said they order mostly all of their 1500's with the 3.92's. Said they have a lot of people come from out of state to buy trucks from them just for that very reason. It wasn't a huge deal to me either way. I certainly wouldn't mind that extra 1-2 mpg with the 3.21's, and I see on here that they perform well, based on some of the trailers I see being pulled around on here. But I'm also not upset with having the 3.92's, these trucks sure scoot! But have nothing to compare it to, never drove one with 3.21.
 

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while there are *a lot* of variables,
your driving environment (city vs highway, average speeds, etc) and driving style primarily,



each increase in axle ratio will hurt your fuel economy 0.5 - 1.0 mpg, so:


3.21 -> 3.55 expect 0.5 - 1.0 mpg lower
3.21 -> 3.92 expect 1.0 - 2.0 mpg lower


I enjoy my 2WD V6 8-speed 3.21:

at 55 mph it's idling along in 8th at 1250 rpm, getting 30+ mpg ...
 

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I have a 2015 Ram 1500 Rebel which comes with the 3.92 gears and have owned the truck for just over a year but just recently my mpg have dropped and have noticed I’m only getting like 5-6 mpg at around 10-25 mph and it doesn’t matter if I’m on the gas or not.
 

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If you're getting 5-6 mpg, there's an issue that needs addressing. Spark plugs? Air filter? any DTC's?
 

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I’m thinking it’s probably the torque converter because it’s not kicking back any codes the air filter is clean, but with the shifting hard issues and the crazy lurch forward when I put it in park like someone hit me from behind a few months prior to my mpg issues
 

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I have a the 6 speed with 3.55 gears and it's adequate for my weekly work needs. I was after a truck with 3.92's but couldn't find any at the time for under $30k so I settled on the 3.55s and get 19mpg easily on the highway at 65mph, at roughly 1600rpm in top gear. Even hills aren't often a problem as the 5.7 pulls strong even with a light load in the bed without needing the trans to downshift to maintain speed. With the 8 speed I would consider the 3.21 gears easily.

I think Ram offers the 3.92's as an option to stay competitive with tow ratings, etc. If you were using a half ton to tow more than 4 tons on a regular basis you would be wise to step up to a 2500 or heavier truck which come with 3.73 gears and 4.10 as an option depending on configuration as it's better suited to tow heavy loads.

I have a 2015 Ram 1500 Rebel which comes with the 3.92 gears and have owned the truck for just over a year but just recently my mpg have dropped and have noticed I’m only getting like 5-6 mpg at around 10-25 mph and it doesn’t matter if I’m on the gas or not.
To add, I wouldn't rule out a dragging/sticking brake caliper. Lower speeds will net lower mpg as it is unless you can get to a speed that allows you to cruise in a higher gear. In town my 5.7 gets 10-12mpg but that's between 0 and 40mph on a regular basis with a light load in the bed (500lbs) and 3.55 gears. 3.92's should net you better mileage in town as it takes less throttle to get up to speed, and 25mph ain't all that fast.

Other things to look at include checking all fluid levels, including the axles as low fluid can cause added drag; clogged cat converter can also cause crap mpg at all speeds; depending on mileage new plugs might be required, or checked for proper gap; and usually some of those things will throw an engine code.

Bad city mileage usually means bad highway mileage. To test, take a short trip somewhere at 60-65mph and calculate what you get on the highway, if it's over 16mpg you have nothing to worry about. 16mpg may seem low but it's not far off what I would consider 'bad' mileage on the highway for a 5.7 regardless of gear ratio. If it's below 16mpg then something is probably amiss.
 

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I had a 2012 1500 Bighorn CC SB, Hemi w/6 speed and 3.92. Ah, those were the days. Man I miss that truck! Avg combined mpg 17 and consistently 19-20 highway. My next Ram will definitely have 3.92’s.
 
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