How big are the rear blocks again?

 

OEM are 1 1/4".

 

They are about 1.25"
I took mine out and I love the more leveled look it gave it.

 

Same here. I'm very pleased with the look of mine as well. Easy leveling mod too.

 

What are the disadvantages of pulling those blocks out??

 

Makes it look more like a low Chevy.

 

Another benefit is that my tailgate loading height is almost 2" lower. So it is easier to lift stuff into the bed and also easier to reach over the sides of the bed rail.
I like the look of lifted trucks but like the functionality that was gained by lowering the rear.

 

Can't think of any, other than if you take the 4times4 sticker off as well, you might get an argument from some lowlife that swears you don't have a 4by. Ya, I used lowering shackles, but actually had that happen. Some peoples kids.

 

Increased stopping distance at higher speed.

Same thing as taking off the front spoiler. People say "I get the same mileage as with it on."... It is there for ground effects, not for looks or not much for aerodynamics. Leveling and/or taking off the front spoiler may have their advantages but they are there for a reason. They help keep your truck on the ground. All vehicles act a bit like a wing as they go thru the air, especially at higher speeds. Adding some downward force with a front spoiler or overall forward tilt helps create a vacuum or suction under your truck that keeps you on the ground. Test out the stopping distance going 80mph with and without the rake and spoiler and you may see the difference between life and death. IMHO.

 

Maybe you were being sarcastic but..
No the back end of the truck does not need to be up higher to act like a wing.
The 2wd trucks don't have the block and sit lower in the rear and they handle and stop just fine.