WOW, are you referring to mpg for a 4x4, because the best I did before LPG was 17-18 hwy and averaged 12-13 just around.
But my "city" driving is 90% up and down dirt paths/roads (stuff that doesn't show up on google maps
) and 10% up and down the so called highway.
I understand that gasoline is better and I lose HP/mpg with propane but this is normal operating procedure down here. Heck my landlord has a $60k Lexus SUV with a $2k direct injection propane system and has no problems with it, not even one code/engine light.
I mostly use a light foot and rarely get it to 70 mph so I'm trying to consider all options to get the most out of my KJ.
I'm not sure what engine destruction you're referring to by running alternative fuel and I'm sure Lovato and Romano (2 big LPG system companies) would disagree with you. I'm told that there are even some benefits like that it burns cleaner and keeps the cylinder heads cleaner, also been told that I won't need to change the oil as frequently. But I'm not sure about this.