I thought they were all aluminum? Mine is. I've tried sticking a magnet to the outside of my pan and it doesn't stick... The guy who owned the truck before me must have done some tranny and rearend work for towing. He put in 4.10s, maybe a shift kit, and trailer brakes. Its weird... But now that I think about it--they do have to be steel because whenever I have done a shift kit or helped change trannys on other people's trucks, the donut magnet inside the pan has to stick to something... DER DER DER!!!!