You're probably right that it is better to use a diesel fuel additive, but you are 100% wrong that trans fluid is not a lubricant. Like motor oil, it is made of crude plus additives. IE, it is virtually the same thing as motor oil, though it has more additives; mostly more of the same stuff, just in different proportions. If you look inside of your Ford C-II power steering pump you will find that it is a high-friction design with slippers on a rotor running around inside a cam. If trans fluid were not a lubricant then the pump would grind itself away in no time. (Conversely, if you run your P/S pump empty, you will destroy it in fairly short order.)
Diesel fuel has had lubricity additives since it became low-sulfur. So you really shouldn't need to add anything... but adding motor oil or trans fluid certainly should increase the lubricity of your fuel.
