Ratio for rear axle code on door says 45/differential D12-rear gawr2900?

Should be a tag on the rear end cover bolt.

Call dealer, parts dept, with the last eight digits of the vin. Parts dept. can tell you what ratio and type it came with.....if you have the cover off, can divide the # of teeth on the pinion gear into the # of teeth on the ring gear for the actual ratio....