6.4 with 8 speed?

SKS 800

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Hemi 6.4
In tow/haul mode only 8th gear is locked out.
I had a 2018 6.4 with 4.10’s and now I have a 2021 6.4 with 4.10’s. There is no difference in fuel mileage from the 6 speed to 8 speed.
However, the 8 speed is better than the 6 speed when pulling. I have a 33’ fifth wheel that is 12,000 wet and it pulls well. There’s some good size hills where I’m at and the 6 speed would be in 3rd and the 8 speed is in 4th.
 

Bearcatrp

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Thanks SKS. Helps me feel better on my up coming purchase. Now to find it before the trade ins drop in price. Missed one by one day.
 

OC455

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5.7 Hemi Big Horn, 6.4L Hemi 3500 Longhorn Mega cab
My dually has the 3.73 gears, 8sp and the 6.4. If I had the 4.10's it would probably net me another 1600-1800lbs of towing capacity. I'm at 13792 lbs with what I currently have, plus 6292 lbs of payload...

If I was going with a big camper/5'ver I'd get the diesel, but considering I only go within state right now, and I'm not going more than 2 to 3 hours away most times, the 6.4 is fine for what I have. Even if I get a 5'ver it will be a lighter one. (Less than 10k)
 

Firebird

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In tow/haul mode only 8th gear is locked out.
I had a 2018 6.4 with 4.10’s and now I have a 2021 6.4 with 4.10’s. There is no difference in fuel mileage from the 6 speed to 8 speed.
However, the 8 speed is better than the 6 speed when pulling. I have a 33’ fifth wheel that is 12,000 wet and it pulls well. There’s some good size hills where I’m at and the 6 speed would be in 3rd and the 8 speed is in 4th.
In tow haul mode, mine will still shift into 8th in the right conditions. However, I do live in flat Florida
 

Riccochet

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2020 2500 Laramie Longhorn
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6.4
In tow haul mode, mine will still shift into 8th in the right conditions. However, I do live in flat Florida
Same on mine. Also depends on what I'm towing. With my TT it rarely sees 8th, but with my bass boat it'll hit 8th no problem.
 

KKBB

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Oakland Ia
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2019
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6.4
Same...mine will hit 8th also, but it is only on one stretch of road that is slightly downhill for about 2 miles. After a mile or so it becomes less downhill, but is still downhill a bit and immediately jumps to 7th
 

HEMIMANN

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In tow/haul mode only 8th gear is locked out.
I had a 2018 6.4 with 4.10’s and now I have a 2021 6.4 with 4.10’s. There is no difference in fuel mileage from the 6 speed to 8 speed.
However, the 8 speed is better than the 6 speed when pulling. I have a 33’ fifth wheel that is 12,000 wet and it pulls well. There’s some good size hills where I’m at and the 6 speed would be in 3rd and the 8 speed is in 4th.

Is there a big difference in engine rpm between 6 speed in 3rd and 8 speed in 4th?
 

Bearcatrp

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Good question. Looking at max torque for the 6.4, looks like 4000 rpms. Is that 4th gear or 3rd gear on the 8 speed? Can’t find a 3/4 or 1 ton worth a crap with gas and 8 speed. Missed one by 1 day. This market sucks. Dealer keeps pushing me to order one.
 

Riccochet

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2020 2500 Laramie Longhorn
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Is that 4th gear or 3rd gear on the 8 speed?

Both. The whole point of more gears is so the computer can keep the engine in the power band longer. You can stay in the 3500-5000 rpm range easier with 8 gears than 6. So when the trans does up shift you're not lugging as much, or at all, to be in the power.

Gassers make peak torque and power higher in the RPM range than a diesel. And it's not going to hurt that low compression 6.4 one bit.
 

Firebird

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Good question. Looking at max torque for the 6.4, looks like 4000 rpms. Is that 4th gear or 3rd gear on the 8 speed? Can’t find a 3/4 or 1 ton worth a crap with gas and 8 speed. Missed one by 1 day. This market sucks. Dealer keeps pushing me to order one.
Yeah, decent 2500's and 3500's with a 6.4 are hard to find. The chip shortage has reduced most inventories to Tradesman packages, great truck, but not a lot of options.
 
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