If u take example of Bhramaputra mail then after KIUL it's unelectrified & carries diesel loco upto DBRG.
It's difficult to provide details as it will be very lenghty. KIUL-NJP is doubled with a tunnel work just after JMP & BGP-PPT single line but after that there is doubled line upto RQJ. After that there are patches of doubled line & work is going on upto LMG. After LMG no doubling work is sanctioned or going on.
As for electrification, work will only start after doubling is completed between KIUL-PPT. Electrification...
more... work is going on between barharwa-NJP to be completed first there after Upto GHY. After GHY no electrification work is sanctioned.