I have been running my 265/70/16 tires on my silverado since I got it. The truck is supposed to have 235/75/16 tires. I would like to change the gears in the diff to fit the tires I have, and put in a g80 rear locker at the same time. How do I go about finding the right gears?

I would also like to adjust the transmission to run properly with the bigger tires. I think the shift point would be adjusted but I'm not sure.

Can anyone help with this?