Cool thanks. I think that is how I installed it. Hmmm. Not sure what's going on then. Might get tires rebalanced. They threw Dynabeads in them.
On your 98, you probably have the np246 transfer case. Are you running a stock from driveshaft or did you get the double cardan version?
A stock driveshaft is notorious for causing vibration is trucks lifted 4" and higher that are running the np246.