Frontera LPG

Hi all,
I have a 2002 Holden Frontera Manual 3.2l (last model) running on LPG/Petrol. I have been running gas since Jan 06. While the installer took 3 weeks to get it working right, there has been some lingering issues. He said he would get to the bottom of it but I think he has forgotten.

Firstly the "check engine" light stays on while on gas (I expect the exhaust sensor to be the issue here) and used to take 30-40k's on petrol to go off. It now seems to stay on whether on gas or petrol. I guess it needs replacing but that would get expensive doing that every service.

Secondly, the revs are slow to reduce when throttling off and above 3500rpm it just way over revs (not that I take it that far normally).
Has anyone experienced these issues in the Frontera or other dual fuel vehicles. I have heard Patrols may suffer as well. The computer mapping was a big issue to sort out as mine is a manual and uses different cpu's to the auto's.

On a bright note, I am very glad to have made the conversion even though it was $3000. It gave me a longer range and cheaper running. at 60c/l for gas it's way cheaper than $1.35 for petrol. I get about 85% /litre from the gas (was told it would be as low as 70%) and during cooler months, it seems to have as much power.