340 -727 -3000 stall- Vibration under load - Trying to find source

Used to balance at work for industrial applications to 60k. Balance is a matter of tuning for a particular operating range. Every rotating assembly has a "critical" and a smooth range.

Usually automotive has the critical near idle and is not impactful during the higher power range. On higher rpm industrial equipment the critical is often in the mid point of the peak rpm which the equipment passes through as it seeks its full speed. Modern electronic drives often have features to lessen the effect of the critical range by insuring not dwelling or allowing running under load through the critical range.

That said, its pretty hard to offer more than guesses online regarding the OP's problem.