Perhaps the LPG is running too rich if its chewing it.
The young bloke at work got an extra 100km out of the gas on his rangie by learning how to tune it.
You can tell if its too rich,get somebody to follow you if it really smels strong you are putting unburnt LPG out of the exhaust.
Google LPG tuning and you will get the gist of how it all works,it isnt rocket science.
Mark everything with a chemi pen before you adjust anything and write it down as you do it.I bet you get it to drive better and use less,I did on my last Series Landy(202 LPG)
GOODLUCK
Andrew