Take a look at the Tie rod ends, and the control arm ends.....
These can wear out over time and could also cause a front end vibration.
Ball joints and unit bearings can too....
To check ball joints, jack up the front end to get the tires off the ground, then grabbing the tire at the 12 and 6-o-clock position, try and rock the tire like it was on a pivot.
Do the same at the 3 and 9-o-clock positions. if you feel a lot of movement or hear clunking, its time to order parts.
As far as checking the rod ends in the steering linkage, thats a two man job. Have someone turn the wheel back and forth real good, while you examine the rod ends for any excessive play or movement.
Unbalanced tires could also cause some vibrations, looks like those are Les Schwab tires, ...take it in and ask them to check balance on those. (wouldnt hurt at least)
As for fluids and the like, thats a good idea, just for peace of mind. I swapped out both differentials fluids, the transfer case fluid, and of course did an oil change and tune up.
The 4.0L Engines dont like fancy spark plugs, so stay away from the platinum's, and E3's and the like. Plain ol copper plugs seem to work best in a lot of our engines.
Axle and Driveline U-Joints are another thing that if replaced now will give you some peace of mind on the trail..... especially if you dont know if/when they have ever been replaced.
