LPG Staggers When Slowing

[Robe]

More often than not when we slow down at an intersection the motor begins to run rough. It staggers, loses responsiveness and sometimes stalls.

This only happens when I am on gas. With petrol there is no problems.

I can prevent this from happening when on gas by manualy down-shifting the automatic gear selector to "second" just before the revs drop too far.

This a dual fuel 1999 AU wagon that has done 250,000+ kms and exhibits no other problem behaviour. It starts fine and idles smoothly.

I keep the petrol tank dosed with injector cleaner and switch to petrol from time to time when at highway speeds.

Any suggestions?

Thanks