I'm 99% sure you have a 4.10. But if you want to be sure you use my caveman guestamation method. First jack up the rear end. Make a mark on the driveshaft and tire. White chalk works best cause it's easy to see and remove. Put tranny in neutral. rotate the tire one rotation and count how many times the driveshaft makes a full rotation. 4.1 times for 4.10 rear 3.7 for 3.73.
