I change mine every 10,000 miles but i run schaeffer's oil in my truck.My buddy has a 96 2500 with the 350, I like it but it’s only 2wd. My trucks and tractors have to be 4x4 lol. He was upset when I had to pull him out of my backyard with my 4Runner. I didn’t know his truck was 2wd, his trailer tire was in a rut and he couldn’t move.
More oil, lower operating temp and extended oil change intervals would be my guess.