I would say to check the converter to flexplate mounting.
If this is a new converter (to you?) it could be bolted up crooked.
Unbolt converter from flexplate and push converter away from flexplate.
Start engine and see if it still vibrates?
Check the flexplate while under there to see if there is any noticeable problems. (bent/crooked, holes wallowed out, etc)
When bolting back up, make sure the converter is pulled against flexplate evenly and tighten bolts without cocking the converter as it is rotated.
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John Wallace - johnta1
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