Elusive vibration

[Mrkentee]

I have a vibration/shake under a load at around 20 psi boost at around 1300 RPM. If I down shift and bring the RPMs up, it smoothes out. As soon as I let off, it’s gone. Sometimes accelerating up to 28-30 psi boost it’s gone/can’t be felt. Just replaced all 6 injectors due to age, and hoping this might go away. Could this be caused by dirty/worn fuel or timing actuators?
Idles smoothly but shakes a bit at 11-1200 rpm.
Rear motor mounts are one-year-old. Fronts are original.
Crankshaft dampener is about three years old.
Driveline has all been gone through.
933,000 miles.
2010 CM 871