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Discussion Starter #1
Alright my question is pretty basic. Why am I taching at almost 2000 rpm while in 6th gear cruising at 70?

Does this seem high to anyone else? And what is the optimal rpm for fuel efficiency?

Stock sized tires BTW.
 

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seems high

That does seem high. Mine is right at about 1650 at that speed. I have same gears too.
 

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You sure you have 3.55s?
 

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on my 97 with 355's and stock size tires I turn about 2000
 

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I'm pretty sure Im also taching around 1650 at 70 with my 3.55 and 20" tires in 6th gear.
 

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Hmmm, spent yesterday afternoon on the Pa Turnpike @ 70-75 and was around or below 1800 IIRC. I have the 18" wheels with Michelins. Pretty sure it wasn't near 2k RPM considering the truck averaged 19.3mpg for the tank with 2 regens.
 

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I checked

I'm running 3.55 and 20 inch rims with 35 toyo mt and I'm right at 1650 or 1700 at 70 mph. I took a close look coming home to make sure!
 

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Discussion Starter #11
Everything i have on my truck says 3.55 gears- Oasis report, and original sales stuff. I bought the truck used, so it is possible they re-geared... Its 4x4 so if they did i sure hope they did both differentials.

I don't know why the rim size matters, but they are 18's with the stock tires. approx 32"?

Does cruising at 2k Scare any of you guys? seems like 1600 RPM would be more efficient.
 

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3.55 rear with stock 20" rims and michelins. 70 mph...~1600-1700 rpm.
 

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Everything i have on my truck says 3.55 gears- Oasis report, and original sales stuff. I bought the truck used, so it is possible they re-geared... Its 4x4 so if they did i sure hope they did both differentials.

I don't know why the rim size matters, but they are 18's with the stock tires. approx 32"?

Does cruising at 2k Scare any of you guys? seems like 1600 RPM would be more efficient.
Rim size matters because trucks with stock 18" rims and tires have a little shorter tire than a truck with stock 20" rims and tires
 

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When I first read this post I thought damn that's high. My 2012 IM 1650 at 70 in 6th gear with 18 " wheels stock tires 3.55 gears.. This weekend I was driving my 97 7.3 with 4.10's and at 70 I was almost kissing 2500 with 33" tires.
 

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Biglain are you sure the transmission is going into 6th gear and torque converter is locking up. Just trying to make sure it's the gears and not some kind of problem in the trans!
If they changed the gears you may want to get some taller tires but 2,000 RPM isn't that high and may be better for towing heavy loads!

Do a google search and find out how you count the driveshaft rotation to tire rotation to check gear ratio.
 

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My guess is maybe the truck came stock with 20" tire and wheel package in which the tires were approx. 34.1" tall. If you are running a 2" shorter tire you will be turning more rpm at highway speed than stock. Also your speedo would not be accurate. Just a guess, I used to be a tire guy. Good luck figuring it out.
 

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Discussion Starter #18 (Edited)
I have deleted this post.
 

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Good job Biglaing that was dedication at 3:00 AM LOL. Glad you solved the mystery!!
 

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Discussion Starter #20
3am for me is 5pm for most people. (I was just leaving work, and had a co-worker help me out)
 
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