Outer Limits 4x4 Board

I have 90 GQ with a 305 Chev. The motor is standard except for a light cam on it. It runs of pure LPG. I currently live in Penrith, Sydney. On the weekend I went up the blue mountains to lithgow and oberon. While up there the car felt slugish and it miss fired and back fired in 4th and 5th gear on the smallest inclines where in penrith it would just power up not needing to go back to 4th or 3rd.

I will know more next week when I start driving to TAFE everyday but it did feel better when I was back home. What is the couse of this?

Is it the altitude. Lithgow is about 1100 metres above sea level. If so how can this be fixed? Thanks

Probably a better place to ask this is in general tech as it doesent sound like it is a problem with any nissan bit. As not as many poeple look here. Plus there is alot of fj40 guys with V8's they maybe able to help.

could be difference in altitude ... timings out?

my bike runs good down here .. but when we get to the top of the mountains its a bit off and noticeable

Regulator diaphram.

Bazzle

air thins sufficating it?????

pretty much .. not getting a clean burn
unburnt fuel going through ... hot exhaust go bang

Thanks guys I will keep looking around for a solution

Sounds like a typical Chev to me. My ski boat has never been any different!!!!!!!!!!