Injection pump ?

[SD Blue]

Recently, I have noticed a vibration that has taken a turn for the worse. This problem would be very random a couple of months ago but is constant now.

The problem is definitely rpm related. I notice it at about 1700-1900 rpm. Below and above that rate it smooths out. Also, I am hearing very severe nailing, and smoke, at lower rpms especially at cold idle. At higher rpms, such as highway speeds, it is not as bad but I do seem to notice a "missing" especially with the car loaded with passengers.There is no increase in oil consumption or blow by.

I am picking up a mechanics stethescope to try and do a little more pinpointing. I tried a large screwdriver but with its decreased sensitivity, I am unsure what "normal" sounds are.

From scratching my head and reading about this, I am thinking it may be the IP. I am suspectiing maybe governor flyweights or something in that area. How difficult is it to access that part of the IP? Any other thoughts as to what I should check?