i have a 49 chevy pickup with a 69 nova rear and front end. i have vibration in the seats and etc. it is more noticable at around 40 mph and above. it is not a bad vibration but iratating. i have had a new drive shaft made at a machine shop and still have the same problem. can it be in my rear end. also what gears will be best in the rear end for street and highway 308 or 342.