I am doing my rear shocks on my 06 4x4. The bottom nut/bolt are both 21mm, what is the top bolt? Is it 21mm also? What is the best way to get to it cuz the frame rail is in the way... a ratchet with an extension?
Also, it looks as though the top nut is "captured" so you shouldn't need hold it, correct?

 

I have an '05, 4X2 and did mine a few days ago. mine were 21mm for both the top and bottom. It "looked" as if it was captured, but it wasn't. On the drivers side, I had to lower the spare out of the way, held a wrench to the nut while my buddy cranked on the bolt, through the wheel well using a 4in extension. Break free or WD-40 the day before really helped. But again, mine is 2wd...hope this helped and good luck!

 

I used a long-reach box-end and then an air-ratchet. The nut is not exactly captured - it has a flange welded on so it can't just spin. The flange contacts the underside of the bed and can't turn. Lotsa folks have had trouble with this. Fortunately, mine went like cake.

 

Did it today on rear. Not fun for 4 little bolts. Bad news is I have to redo it all over because I either didnt get the new rubber gromets with order or forgot to reuse old ones. Used a 15 mm racheting wrench on my model. What shocks you using. Jumping on the back end after replacement is amazing now. Used KYB Mono shocks.