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Discussion Starter #1
I suspect my used JKUX previously had larger tires on it...here's why.

It hesitates to down shift when going uphill and trying to keep up with my other Jeep caravan members. The speedo also seems to be off by +/- 2MPH.

Last night when I was trying to do my final bed-in process on my brakes, it was damn near impossible to quickly accelerate from 20 to 60MPH and it was reluctant to shift when really hammering on the accelerator.

Could I also have different gears and how would I be able to tell?

What do I need to do to investigate these possibilities?
 

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The Bad Guy
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I suspect my used JKUX previously had larger tires on it...here's why.

It hesitates to down shift when going uphill and trying to keep up with my other Jeep caravan members. The speedo also seems to be off by +/- 2MPH.

Last night when I was trying to do my final bed-in process on my brakes, it was damn near impossible to quickly accelerate from 20 to 60MPH and it was reluctant to shift when really hammering on the accelerator.

Could I also have different gears and how would I be able to tell?

What do I need to do to investigate these possibilities?
You can get the gear ratio by raising the rear of the ground and count how many times the drive shaft turns for 1 complete tire rotation.
 

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Did you buy it from a private owner or from a dealer? Either way, if the gears were changed do what daggo mentioned. If you purchased it from a dealer, even if adjustments were previously made, their Starscan tool should be able to bring it back to the stock settings. Just make sure you know what gear ratio you currently have in case they were changed from stock, which with an X it would be 3.21 or 3.73 (optional) from the factory.
 

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If one has already been used he may not be able to.
I dont think it works that way, but I could be wrong.

The tuner gets vin locked, not the vehicle.
 

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I dont think it works that way, but I could be wrong.

The tuner gets vin locked, not the vehicle.
True, but now there is no Stock File for the Tuner to Copy, if the OP gets a new one.

So now the Stock File is the Tuned File that is still possibly in the OP's Jeep.

But...I could be wrong too. :atomic:
 

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True, but now there is no Stock File for the Tuner to Copy, if the OP gets a new one.

So now the Stock File is the Tuned File that is still possibly in the OP's Jeep.

But...I could be wrong too. :atomic:
The dealer should be able to flash it back to stock
 

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Discussion Starter #10
Thanks for the replies...I need to get it serviced soon, so I will have the dealer check it out. I like the easy recommendation to count the rotations of the driveshaft.

Thanks all. If there is more to know or check please keep the recommendations coming.
 

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True, but now there is no Stock File for the Tuner to Copy, if the OP gets a new one.

So now the Stock File is the Tuned File that is still possibly in the OP's Jeep.

But...I could be wrong too. :atomic:
I dont believe we are talking about a tune, we are talking about values that are changed in the PCM. I am under the impression that changing the tire size doesnt rewrite the entire tune, like a performance tuner would.

But once again I could be completely wrong:lmao:
 

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I dont believe we are talking about a tune, we are talking about values that are changed in the PCM. I am under the impression that changing the tire size doesnt rewrite the entire tune, like a performance tuner would.

But once again I could be completely wrong:lmao:
You're not wrong. It doesn't. IMO the best thing for the OP to do is make sure what the gear ratio is in case it was re-geared by the previous owner, and to have the dealer use the Starscan for any changes that are required back to stock if that's what the OP wants. I don't think the OP mentioned what size tires and wheels are currently mounted at this point which is important as far as the trans. shift points, along with the gears if that applies. There's also the possibility that the trans. issue isn't a program problem but a mechanical fault. Since it's going to the dealer for service they should be able to take care of it. However, the trans. could still be a separate repair.
 
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