Hey guys, i am thinking about changing my diff gears in my XR8 ute from the 3.45's to 3.9's, the ute is auto and i need something to get it going a bit quicker and to help with towing.

other than the obvious swap what do i need to do with the speedo to make it read properly and shift at the right points? Ive heard there isnt a speedo gear up to 3.9?

Will the electronic speedo corrector from jaycar work? or will it just be a headache?

The diff is only 20,000km old which i had Northern differentials build a new one which was in my manual XR6 ute, so i swapped the diff's over from the XR6 to the XR8 as they were exactly the same setup, only one was woth $2500 so i wasnt selling that only to have the XR8 diff go. bit of piece of mind

I just bought a 3.9 diff with an auto so im interested to know as well.