With 3.73 gears, and for any given road speed, the driveshaft is turning 11.4% faster than with the stock 3.27 gears. In 4th gear at 80 mph this would be 4000 rpm with the 3.73s versus 3500 rpm with the 3.27s--500 rpm faster. Spinning the driveshaft faster can exacerbate imbalances and/or create sympathetic vibrations that were not previously apparent.
This can worsen if the driveshaft was not remounted to the rear end drive flange is the same relative position as before it was dropped to change out the gears.
- 2003 GT, UPR X, FRPP 24lb/h, Magnaflow, PP 70mm TB & plenum,
Delta Force tuned, Steeda UDPs, Ralco flywheel,
RAM HDX clutch, 3.73s, 262 rwHP/305 lb-ft.
New ride (7/1/2013) 1998 Mercedes SL500-5.0L 32V VVT 326/347 HP/tq
Engineering is, at its base, making what you want from what you have.
At its extreme it is making what you want from what you can get.