How do I determine which rear end gear is in my chevy trailblazer?

I'm looking to buy a used Chevy trailblazer. I know that Chevy used three different rear end gears in the trailblazers. Most of my driving will be around town, so I want the gear that will give me the best fuel mileage. How do I go about determining which rear end gear is in a particular trailblazer?|||Open the glove box and look at the codes.


GU6- 3.42


GT4- 3.73


GT5-4.10


G80- locking rear diff|||the 3.42 will get better becasue ur rpm will be lower at higher speeds|||You can also ask the parts counter at the dealer and give them the VIN and they will tell you.