I realized the day I changed this out that I had put about 20,000 miles on it. I changed it out when I got the car at 62K; don't remember the fluid the P.O. had ran, but he said it was all full syn. So part of it could be cleaning the old fluid up some if it wasn't the best stuff. I think my original thought was the 25K interval spec'd for normal service. 15K is severe service, IIRC, so I'm shifting to that. On a related note, I change my tranny fluid out every 10K or so, because I've found that the GMSMFM breaks down around there to the point that the buttery smooth shifts it gives aren't present. Honestly, it's really closer to 5K that it's not as good. I may try AMSOIL's fluid next, but I've got 5 quarts of GM still in the garage...