Others can correct me if I'm wrong, but with the Gen 2 4-wheel system, your front driveshaft is not turning if you're still in 2 wheel drive with the factory system. The front axle disconnect system [CAD as posted by others]allows this to happen. So, only your rear driveshaft u-joints would be a cause for concern if you're getting vibration while driving, front's should be ruled out if you're still in 2 wheel drive.
That being said, check ALL the drivetrain mounts, I've had strange vibration issues due to wear in some of them. I've replaced the T-box mounts, and one at the front diff.
Also check the front crankshaft pulley bolt at the engine, I too have had vibration -on-acceleration issues from the engine when my "second issue recall bolt loosened up" and once I replaced the crankshaft pulley bolt and pulley with the latest stuff from Mitsu, that too went away[seriously, 3 mods to one crankshaft bolt <img src="/forums/images/graemlins/angry.gif" alt="" />, I mean <img src="/forums/images/graemlins/rolleyes.gif" alt="" />]
Anyway, there's a few more things for you to check. Let us know what you find