Will I need a new tune??

[Jackpine]

Then I have to say you DO want new tunes. Sorry!

With the new gears your speedometer and odometer will be "off", which is no HUGE deal, but your shift points aren't right either. They're commanded by a combination of speed and throttle position. So, since the truck's speed is wrong, they happen at the wrong time.

I'm sure it's all something you could live with, but I imagine you tuned your truck for a reason, and that reason is not "halfway performance".

But, I've just had a thought, which may negate everything I've said above. Your truck MAY have a more "direct drive" if that makes any sense from the speed sensor to the speedometer. I'm thinking now that the PCM doesn't even get into the act in your MY truck here, and a tune may not be able to adjust the speed. But, when you get the new axle, they can install different gears on the speed sensor so that it will send correct speed and distance information to - "wherever" (sorry, I'm not really sure how your system works - I know it's not a mechanical cable, but I don't think the PCM controls the speedo.

However, the PCM and the speedo DO get their speed information from somewhere, so all you have to do is make sure that information is correct. If it is, then your tune is fine with the new gears and you won't have any speed or distance errors.

Find out from the shop doing the swap what happens with the speed and distance indications.

- Jack