Hi guys, I am new around here and have some newb questions for you guys.

I have recently purchased an auto 1990 GQ patrol ST 4.2 Unleaded/Lpg wagon.
I have a few questions regarding the longevity of engine components, especially when it is running LPG.
It has low 200,000km on the clock and seems to run well, idle is a bit low on petrol when in gear but runs ok on both fuels but, it is incredibly slow..... I came out of a worked FPV F6 ute and F6X Territory so it is quite a system shock when you put the foot down and you aren't pushed back into the seat like the last 2 cars I owned.
My old man bought a 1990 Maverick brand new and I recall that going quite well, it is specced exactly like my GQ sans LPG.
Would it be a case of it just being a bit tired and it being tuned to run LPG?
Would you recommend getting rid of the LPG system entirely and getting the car tuned to run straight unleaded?
I was also wondering what I need to keep my eye out for in regards to these engines. What are common components that fail, what preventative measures can I take to keep the car running well, and for a long(ish) time.

Also, I want to fit 33 inch tyres to the standard rims but the car is at standard height. I will only be doing "soft off roading" for the time being so I really don't need a body or suspension lift... OR WILL I have to lift to fit the 33's?
I am sure I have seen a standard height Patrol with 33's on it.