vibration after 3.23 to 3.91 swap

Thank you for being gentle...I hope I can return the favor someday

At 130mph my driveshaft rpm with 4.30s was ~7030, but with 3.55s is ~5800; that's a reduction to 82.5%

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You are almost correct; I said TO 82.5%.
What is 17% of 7030? it is 1195rpm, and
What is 7030 less 1195? it is 5835.
Which is not 5800, so you are almost correct.
5800/7030=82.5%
Its like the difference between your gallons and our gallons; yours are 128 oz and ours are 160oz. So yours are 80% of ours, and ours are 125% of yours; which being 25% greater; and not 100% less 80% =just 20%.

Or did I quote the wrong thing