Thank you @dayrider for such a quick response and for a warm welcome into the club - my responses are as follows on your queries/answers:
Did you get it checked from an electrician or assumed this?
Yes - I have checked through an expert and the gauge is not working and needs to be changed.
could be a foundation issue, as rpm is lower on D then on N, you feel it
Have already checked - foundations are perfect. RPM is same almost on both D & N.
That requires proper diagnosing, does the vehicle have any other issues? too much smoke, excessive fuel consumption, high rpms etc?
Well, before going to Naran, it was not smoking but during my ride in Naran, there was too much smoke and engine oil was short which was never a problem in the city. Now I am in routine life and the engine oil is perfectly ok and smoke is also reducing day by day.