Violent shaking John Deere JS20

My John Deere JS20 has been giving me trouble with this for a long time, and now that I've fixed the self propel and replaced the flywheel and key (it was totally destroyed, flywheel spun on the crank) it is still shaking.
It runs perfectly fine, maybe starts and stops a little quicker than before replacing everything, but it runs fine. Only problem is the shaking. I thought it maybe had a bent crankshaft, but after looking at it, I'm not sure that it does. I figured after discovering the flywheel key had sheared off that it was the issue, but the shaking is still there after replacing it. I checked the debris shield under the drive belt, and I cleaned it and tightened it up, so that's not the problem.
Are there any other things that are known to cause this kind of shaking on these mowers? I can't see anything else that could be a problem.

Bent blade, bent crankshaft, or unbalanced blade are your three top causes for the shaking. The flywheel issue suggest that you hit something solid, therefore bent crank is a possible cause.

ILENGINE said:

Bent blade, bent crankshaft, or unbalanced blade are your three top causes for the shaking. The flywheel issue suggest that you hit something solid, therefore bent crank is a possible cause.

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I was worried about that. I'll have to pull the blade and see if that makes a difference. IIRC, it was shaking without the blade off, but I want to double check.