3" seems a little extreme..
IF you do it right, replace the pucks instead of adding on. (Like the previous owner of my Jeep did.) then you should be ok.
I belive the general consensace on here is 1" is fine, 2" is good if it's well done. 3" if your desperate, and anymore is asking for disaster.
if you think about it, how much leverage do you have to put on a Grade 5 bolt to make it shear/bend?
Now you say.. "Oh, but you have the mechanical advantage of a lever/wrench/breaker-bar.
Well, your Jeep may not have that mechanical advantage, but your tub sure has a hell of alot more weight then your arm can put out..
Just think about the kenetic energy. Your cooking along at 60-70MPH, and then the frame stops rather suddenly in an emergency break.. stress IS put on the bolts. (Even Grade 8 bolts.) Eventually you will run into trouble. Do it a few times too many... you get the idea.
So. 1" is fine, most of us have that.. 2" is ok if it's done properly.
Personally.. If I were to do lifts all over again?
I'd go SOA with 2.5" springs, and a 2" body lift. That should be plenty to clear 35/38's..
Beats the SUA 2" shackle, 2" body, 2 odd suspention combo on 33's I have now..