3.09 gear set with 3.23's
I’m still coming up with 9.98?
yes 3.09 x 3.23, I get 9.98 as well, and
9.98/2.66=3.75 so
the 3.09 combo takes off about like a regular 2.66 does with 3.73s
The thing is, lower number gears, keep your engine in each trans gear a lil longer, unless the tires are spinning. The 3.09 low is great in first gear, but when she hits second, the 3.23s take a longer time to hit shift-rpm versus a bigger number rear gear, unless of course the tires are spinning.
Whereas a bigger number rear gear will blast thru the gears quicker, putting down more average horsepower per unit of time, usually leading to a lower ET over a given distance....... unless the tires spin,lol.
On the street you can't get traction unless you spend big coin on the back end, so it hardly matters what rear gears you run. It doesn't really start to make a difference until you start pushing wind at say 85mph or higher.
If I had to guess, I'd say your vibration is caused by driveshaft run-out. The driveshaft machines I have seen, do not spin your shaft to 6000, but maybe to 2000 . It may be in pretty good balance there, but if the driveshaft has a bend in it, it just gets worse and worse with driveshaft-rpm. I had to get mine done 3 times, and on the third time I replaced the tube, and now it's fine. Like you, I spent a lotta hours looking for that hi-speed vibration.
Jus saying.