Jfsram

Check the pinion bearings but most likely it's the driveshaft.

What is normally ok on a 3:1 geared car is not ok on a 4.10 geared car. The driveshaft spins close to Mach 8 on a steep geared highway driven car. Balancing must be perfect.

calinotch

lol so your thoughts is that its the driveshaft? the vibration occurs at about 2500 rpms in 5th so idk what the driveshaft would be runing at that point.

lx5.0

did you ever figure out the problem i have the same problem at the same rpm in the same gear

Jfsram

Are you asking what the revolutions per minute the driveshaft is spinning?

Get to the speed you are concerned with. 2500rpm in 5th gear. Note the speed. Switch to 4rth gear. Continue at the same speed. The tach willl now read higher. It's the same rpms' as the driveshaft.