Driveshaft problems...
 

Every few times I go to the track I seem to get a soft vibration from the driveshaft yoke and get it re-installed at the drivetrain shop. They rebalance it, put new yoke on, and every time a new vibration starts. It seems that the yoke is coming loose? It is a stock driveshaft with the 12bolt yoke on it Anyone else experience these problems?

The stock steel DS's have a problem with vibrations. It was bad enough that there was a factory TSB issued, and some people were able to get free aluminum replacements while the car was still under factory warranty. Attempts at rebabalancing are generally unsuccessful. I believe the problem may have been caused by the input yoke not being concentric with the centerline of the DS.

Most people just opt for a 1LE or LS1 aluminum DS. On the other hand, with enough power to require the 12-bolt, you might want to consider an aftermarket steel DS, like the ones from Spohn or Dennys.

Moving to "Drivetrain"......

I see, so there is a centerline problem, which makes sense with the problems I have had recently. The aftermarket ones you talked about, I will look into those and hope they arent "too" expensive.