If Still anyone having or using LG G3 US990 US cellular model then Fulmics ROM is working perfectly with Jio simcard with DATA and calling Through Jio4G voice.
Issue of low Signal solved with this ROM
Earlier problem of Registering with Jio4G voice is solved with Fulmics ROM.
Other features are also working well and no major issue.
Follow given XDA link for step by step installation of Fulmics ROM.