If you plan to offroad your truck you might be better off with 4". I wish I had a 4" instead of the 2.5" that I have. It would have saved me alot of hassle. If you get springs all around then you should get about 2.5 inches. At first it might be higher, but the springs usually settle. If you get an add a leaf then the rear WILL sag. Trust me, I know from experience. Stay away from blocks if you can.
I have a 2.5" lift, and now I am having to get creative to get my truck higher. 33's will fit fine, and thats all I thought I wanted, but after wheelin with guys with 35's it is the only way to go. So now I have a 1" zero rate from ORD in the rear for about 3" of lift and extended HD front shackles from ORD for about 2.75" of lift. To make room for 35's I will add a soft top which will lift it a little and put a zero rate in the front of my truck to get to 3.5-4" of total lift. Its alot of hassle when I could have just gotten a 4" in the first place.
My Chevy isn't broken, its just out of gas.