8 speed issues? Or normal

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yillbs

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Sup fellas. I'm starting out with , I'm lifted, 6 inches, 35 inch tires. I expect my gas mileage to suck, in fact I've accepted it. Until yesterday. I was driving down the road and noticed I was doing 71 and at like 1600 Rpm and I was showing about 15 on the evic. Amazing right ? I then put my max gear in eight and realized my trans never goes to 8th unless I'm going down a hill. Is this strictly due to the larger tires ? Or is this normal behavior ? The 8speed in my Durango doesn't act like this at all.
 

smurfs_of_war

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Pretty sure that's normal with the size of tires. 8th is pretty tall and it doesn't take much resistance to drop it to 7th or even 6th. What's the diff ratio?

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Markcuda

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Your rear end ratio is now a higher numerical number than stock.
If you have 321s, you may never see 8th gear till 80 plus MPH.
 
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yillbs

yillbs

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Your rear end ratio is now a higher numerical number than stock.
If you have 321s, you may never see 8th gear till 80 plus MPH.

I do have 3.21, I just noticed the magical 15-16MPG in 8th, but i figured it was to good to be true lol. I'll settle with 11-12 for now i recon.

Thanks guys!
 

Markcuda

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I drive 23 miles to work every day, I set my cruise at 54 MPH, if I have any wind at the front or sides of the truck, I will not see the 8th gear.
And I only have the stock tire higth and no lift kit.
 

6.7CumminsDrvr

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The lift and 35's are not helping those 3.21's. As stated above, you might have to hit 80 mph before you'll turn enough RPM's to utilize 8th.

FWIW, my truck sees 8th all the time but I've got 3.92's.
 
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yillbs

yillbs

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The lift and 35's are not helping those 3.21's. As stated above, you might have to hit 80 mph before you'll turn enough RPM's to utilize 8th.

FWIW, my truck sees 8th all the time but I've got 3.92's.

Figured as much. I can squeeze 14 out of it, if i pay attention and drive without the help of cruise control. I actually like the 3.21 setup, it's got the power i want low, contrary to what many, many reviewers have said.
 

Ferro

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I have a 4" lift with 35s. I can do 70 or 80 and it will go in to 8th gear. I have a 321.
 
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yillbs

yillbs

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I have a 4" lift with 35s. I can do 70 or 80 and it will go on to 8th gear.

I can get it into 8th at around 70.. but i can't keep my speed in 8th gear, ECO stops coming on, and it has to change. I think the other guys are right, the gearing is just too tall, and i'll need to be going faster to enjoy 8th.
 

Ferro

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I can get it into 8th at around 70.. but i can't keep my speed in 8th gear, ECO stops coming on, and it has to change. I think the other guys are right, the gearing is just too tall, and i'll need to be going faster to enjoy 8th.

When I am doing 70 it goes in to eight gear all the time with the ECO coming on. When I go 80 it takes a while to go in to eighth but it will.
 
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yillbs

yillbs

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When I am doing 70 it goes in to eight gear all the time with the ECO coming on. When I go 80 it takes a while to go in to eighth but it will.

what kinda MPG do you get in 8th at 70? that seems to be a sweet spot for 35's , i get an extra 2 - 3 MPG, which doesn't seem like much, but when i'm constantly getting 10-11, it helps.
 

Ferro

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what kinda MPG do you get in 8th at 70? that seems to be a sweet spot for 35's , i get an extra 2 - 3 MPG, which doesn't seem like much, but when i'm constantly getting 10-11, it helps.

It says I'm getting 17 to 18 miles per gallon how accurate it is I don't know. And that's in the summer months. In the winter with the additives they throw in the fuel I'm lucky to get 12.
 
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yillbs

yillbs

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It says I'm getting 17 to 18 miles per gallon how accurate it is I don't know. And that's in the summer months. In the winter with the additives they throw in the fuel I'm lucky to get 12.

I've only been able to drive it in sub 50's, winter gas. I'm geting about 12 now, but no 8th gear usually. Thanks for the info, that gives me an idea of what I wanted to know.
 

mh3c

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It's a combo of size, increased tire weight, and 3.21. Not sure you'd see the same with 3.92.
 
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