earlier, JB had Electric from VSKP - TEL section, but the major reason came due to 12806 which used to arrive late with an EMD and TEL which didn't had a proper pit line to hold an electric, the electric loco had to wait until 12806 comes so tat it can attach n take back n the EMD to take 12805.
so SCR decided to fix end to end with Diesel loco as it was easier, but WDM-3A failed too as due to grad reasons in GNT - SC section. finally a message was sent to SCR from RF's only about considering EMD link. hence, KJM allowed its own EMD to run end to end for both trains.
Since...
more... the EMD run, both 12805/06 still face minimal delay at both ends.
Hence EMD is doing a very good work.