Don't overlook the diesel fuel additive that Amway sells. Yes, I wrote Amway, and not Amsoil. A friend's son who is doing the Amway thing asked me to run a winter on it. It is made by Chevron. I found it to be a very good product. Based on the information I could glean, it seems very similar to the Amsoil diesel additive cold flow combo product, but was cheaper by application rate. It is called XLP.
http://schutzintl.com/xlp.pdf
http://schutzintl.com/xlp.pdf