AU S2 Fairmont power issues.

[Crash Lander]

My dad's AU series 2 Fairmont is on lpg. He's had nothing but drama with it. I drove it today, and it seems to be lacking seriously in the power department.
For example, coming out of a round about, dad says to put my foot down. I did, and it dropped into what felt like first, revved t's nuts off, and really didn't display much acceleration, even when it changed into the next gear up. Had we been in my nog stadard AU S1 Fort, we'd have been thrown backwards like a $2 whore!
On petrol, it's not noticeable better either.
He's had it at Ford, and at the lpg guys shopNo-one reakons there's anything wrong. Any suggestions? Car has done 140,000km.
He has it serviced regularly. I am thinking maybe oxygen sensor, as I can't guarantee it's ever been replaced, but I may be clutching straws.
Also, it won't start with the first turn of the key. Mainly in the morning. Second try it's fine.
Thanks guys.