Yeah I did tighten the pinion nuts. After a week, I second guessed myself and pulled both driveshafts off and check them (and restaked them again). However they were already tight. If anything, I over tightened them just a hair to see if there would be any reduction in slop. Since you said that there should be some movement, I would expect this to be normal then.
Should there be any movement at the pinion flange? The front pinion is slightly more loose than the rear diff pinion flange is, as I mentioned in my first post.
I checked the motor mounts a few weeks before I started tinkering with the driveshafts, so I know those are tight and in good shape. I had a bad motor mount several years ago after an accident and that was very noticable and gave a different sensation. The bad motor mount was most noticable when I was idling and revved the engine.
This vibration doesn't have anything to do with RPM's and is present when the hubs are locked and even more so when in 4wd. If there isn't supposed to be any movement at the pinion flanges, then I will probably start there next. I have to pull the front diff back out anyway due to a leak at the bottom of the 3rd (darn Right Stuff RTV).
