I'm using Amsoil in the differential in my Ranger. The fluid was changed based on Ford's maintenance schedule, which said the original fill was good for 100,000 miles. The truck had 101,000 miles when I got it and the change was a few thousand miles later. (In other words, the previous owner obviously had not changed the fluid before trading in the truck.)
This is a standard 8.8" open diff with 3.55 gears, and the truck has the factory tow package. The gears looked just fine after I pulled off the rear cover to drain the diff.
In the past I have used Red Line products. Either Red Line or Amsoil will work just fine for you. What I like about Amsoil for this application is getting a better price as a Preferred Customer and the squeeze bag packaging, which made refilling the diff easy.