8-speed vs 6-speed gas mileage

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Wild one

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If Ram improves its fleet CAFE by 0.5 mpg it is not trivial although it will be for the person who buys the truck. What you get with the 8-speed are two additional overdrive gears which help only when on level ground and no load in the bed or attached to the hitch.
There's not all that much differance between the 6 speed and the 8 speed in regards to the 2 overdrive ratio's in both transmissions,it's the gear ratio's under direct drive (1:1 ,4th in the 6 speed and 6th in the 8 speed) where the 8 speed shines. The 8 speed has a far better torque multiplication factor in 1st and 2nd compared to the 6 speed,which helps get the truck moving with less gas pedal application.

12345678ReverseRangePeak Torque
65RFE3.001.671.501.000.750.673.002.33410 lb-ft (540 Nm)
8HP4.713.142.101.671.291.000.840.673.304.04332 / 516 lb-ft (450/700 Nm)
 

A_mod_too_far

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I have a 13 sport with 6 speed and 3.92 diff. I find that with 87 gas I get 12/16 for my commute. I feel like it is low overall, but I am running all terrain tires so I dont know if that makes a big difference. Supposedly I'm supposed to get 13/19 but the highest I've ever been able to get is 17.5 in perfect conditions.

As far as the 6 speed goes, I had to have it rebuilt at the cost of 3k this summer because the pump was bad due to the abuse of the previous owner. But now that it's working and upgraded, I have nothing negative to say about it. I believe it being a simpler transmission there are more shops willing to work on it verse the swap shops that try to sell you a reman unit for 7k
 

Dusty

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I can offer a comparison of the affects of the transmissions being discussed based on my previous two 1500 Big Horns, both Quad Cab, two-wheel drive, with 3.92 axle ratio and 20 inch tires.

My 2010 had the six speed and finished a lifetime average of 17.67 MPG at the end of four years, 104,000 miles. I had 20 tank fills that averaged 20.0 MPG and over (highest recorded was 24.01).

My 2014 with the 8-speed finished with a life time average of 18.64 MPG at the end of four years and 94,000 miles. I had 52 tank fills that averaged 20.0 MPG and over (highest recorded was 25.81).

This represents only one person's driving habit, style and topography. Your mileage may vary.

Regards,
Dusty
2019 Ram 1500 Billet Silver Quad Cab 2WD, 5.7 Hemi, 8HP75, 3.21 axle, 33-gallon fuel tank, factory dual exhaust, 18” wheels. Build date: 3 June 2018. Now at 79608 miles
 
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