Almost everyone who does the swap complains about vibrations. I don't think its a coincidence.

No, the driveshaft is custom, but if it were the culprit, it would not just show up under load.

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For Sale: 1982 MB 300TD
1995 Chevrolet Suburban 6.5TD

Sold: 1980 IH Scout Traveler- Nissan SD33T Diesel