I have never tried it... I don't ever expect to gain any MPG by adding a fuel treatment. I do expect the additive to clean and keep my fuel system clean, as well as lubricate my fuel pump and injectors. With that said, there are only 2 additives that I use in my 7.3L
1. SoyPower-->{soybean oil}-->Outstanding Product!
2. FP60-->Lube Control reformulated this product about a yr ago. They realized how well a soy based additive mixed with either gas or diesel cleans and lubricates your fuel system. IMHO-->A clean well lubricated fuel system as well as a well maintained auto will get the best MPG, without modification. JMHO.