Whatsup , im looking to swap my rear differential on my 2006 5AT G35 coupe to one with higher gears, would a g37s automatic differential with 3.7 gears fit mine? If not which ones would?

The later model automatics have different flanges and a longer shaft. Look for one off of a manual.

Are you looking into swapping diffs purely to increase your gear ratio, or is your stock diff already blown and you're just looking for other alternatives along the way while replacing it?

Be aware that taller gearing will make your car significantly slower. It will also make your speedometer/odometer read low. I'm not sure that you'll have much luck finding any cheap alternatives for taller gearing. Most people usually modify their gearing in these cars to be lower, not taller. Lower gearing equates to better acceleration off the line and at low speeds but decreased fuel economy and increased cruising RPMs.

There are aftermarket final drive kits out there for G35's and 350Z's but they mostly go for lower gearing, not higher and the kits alone cost upwards of $500 alone in parts and require some precision machinery for installation into the diff.

If your goal is just to swap in another diff. to save some RPMs while cruising or increase your fuel economy, it's not worth it even if you can find an option for viable gear swaps.

The ATs have somewhere in the ballpark of 3.3.
By moving up to 3.7, he's going to have shorter gearing, therefore better acceleration.

Just so you know, G37 with automatic trans had 3.3 rear ends and the driveshaft flange is different. The G37 6MT has 3.7 gears and the correct flanges to bolt up.

^Some automatics had a 3.7 as well. The first diff I bought was from an auto, requiring me to swap flanges and shorten the pinion shaft.

Forgot about that, the 07-08 G35 5AT autos did have the 3.7 diff, when they changed to the 7AT is when the diff dropped (raised?) to 3.3.

so if i got the g37 6mt rear end would i have to buy anything else to make it fit or just swap the differentials out

^It would be a direct fit
You were right. I forgot that diff did come off of a G35S.