2005 Chevy 1/2 ton with 14 bolt 4:10 differential. I tow a lot and change fluid every 15-20k. I use Lucas 85-140 gear oil. Other brands always leave a gray powder all over the bottom of the case that is metal wear. Amazingly, with Lucas gear oil the gray powder is hard to find. I'm staying with Lucas, it really works. -Warren W., Mesa, AZ