Yeah, Ive done the ATF in the diesel fuel filter too. It really does a good job of cleaning the diesel injectors and the combustion chambers. When I used to work on construction equipment, it was common practice to use ATF in the filter. Not so much in the on the road equipment, the Atf returning to the fuel tank would stain the diesel fuel red, making the fuel look like off-road diesel. DOT would drop the fine on us quickly for that. I wouldn't suggest it in today's modern diesels though. The particulate filter in the exhaust system might not react well to ATF residue.