if you want articulation, it is important not only to fit the tires, but to make sure they have room to travel as well... 2 very inexpensive way to help your articulation would be to remove your rear tracbar and get a set of swaybar disconnects... both the tracbar and the swaybar do a lot in keeping your axles level, and if you can disconnect them, you will have a much better chance of keeping 4 on the floor on uneven surfaces... as far as the shackles go, you don't have to get greasable shackles, but it does help in the smoothness of your ride... i've done a few shackle lifts, and never have i used the greasables, and i have never come across a problem.
if you want better shackles, and want GREAT articulation, you can go with a revolver shackle, this allows for an added 9" of drop in your wheels.. and will add about a quarter inch to your clearance