intermittent missing fault in lowrange

[Deadduck]

Hi I have a suzuki vitara 1994 g16b nz new market. I have a weird missing fault in only lowrange high range and 2wd are fine so when I'm driving along in the bush at a mid - slow pace i will have my foot down enough to just where it is keeping a constant speed and it will all of a sudden miss for a few seconds then come back in and it will keep doing that I have the hotwire mas that has been changed so i know its not that has a new 02 sensor done one old one as well im just not sure where to go or what to test next timing is all set correctly.
Thanks