we have used Amsoil products for years in our race cars. I became a believer in their product around 1977. I had an old bronco that had to be bump started. (to lazy to fix starter and had a hill for a driveway. lol). starting it was never a problem till cold new england winter came. anytime temp got to 10-15 below, the car wouldn't roll. then changed to amsoil synthetic gear lube in both axles, and used their grease in all u-joints. could not believe how easily the car rolled. I was a believer from then on. using it in the racer showed lower temps in rear gear, even when we moved to the dessert and raced.
to be fair, I also used mobil 1 for a while when I picked up a sponser.