About 80% f the time when I am about to drive off after stopping, the first gear doesnt want to kick in. It hesitates and sorta revs out but doesnt actually accerlate at normal rate. Then it will kick it and be normal. Only happens on first gear and 95% of the time its on the LPG. I had my mechanic check and tighten my leads, but could it be the gearbox saying bye bye?

highly likely its the gearbox!
Thats what mine started to do and it was knackered!

Make sure there's plenty of fluid in it (before it's too late).