Dan,
Propane is like nitro for diesel. It's an injection system that is set to come on a predetermined boost level. What is does is allows for a complete burn of the diesel when mixed with the propane. I needed some extra power for pulling hills and didn't want the extra egt's and didn't want to spend the $2k to put on a banks system or something like that. With the propane system it actually lowers your egt temps. and increases engine life. When not pulling hills the truck has all the power I want, it's a Ford powerstroke. I wanted something that wouldn't hurt mileage and I could use just when I needed it. The propane system was perfect. You can set it to run whenever you want to. I get about 2 miles better per gallon when pulling which when figuring in the cost of the extra propane gives me a net gain of .7 miles per gallon. The cost was only $399 and for me it works perfect.
Richard