Does my driveshaft need to be re-balanced after changing the slip yoke?

I got my Tremec 600 installed the other day. I've put about 100 miles on it so far. Today I got it up on the highway and noticed that I have a vibration and some sort of noise around 75-80 mph. I'm thinking it's my driveshaft, but I'm not sure. It is an aluminum one, but I'm wondering if changing the slip yoke threw off the balance? Anyone had a similar problem? Any idea on what it would cost to have it re-balanced? I figure it couldn't hurt either way.

Thanks, sounds like it will be an easy fix then hopefully. What did you pay to have your D/S re-balanced? I'm gonna have to call around tomorrow and see who does it local. Gotta get this thing fixed so I can go rack up another 400 miles, then have some fun!