Since I have had my gears changed from 3.00 to 3.70 I have noticed a lot of vibration at speeds around 80 mph. Since traffic on most of the freeways around here travels at this speed, I am feeling vibrations OFTEN. I've had a couple of mechanics look at my car and they both seem to think this is due to the more aggressive speed my drive shaft is rotating to attain this speed. So my options are a. Have my drive shaft balanced or b. Buy an aluminum (already balanced) driveshaft. If there isn't a significant performance difference I'd like to go the cheaper route. If there are real differences, I don't mind spending the extra. Also I will be building a 342 this summer and expect to be around 340-350 rwhp. That said is this amount of hp going to be detrimental to either setup??? Appreciate the help in advance.