Not many run it none that I know of. As far as power they say it adds up to 100 HP , I never got close when I had a propane system on my truck IIR is was more like 50. I only ran it for added power not for MPG so I have no data but I assure you that the gains if any would be minimal. You'd get better running a tow tune as by the time you figure in the added cost of the propane at fill up.
I wouldn't bother. If it was worth it believe me more would be running it.