Do not get the 5.3.... They are crap. Mine burns a quart of oil every 1500 miles. GM says it falls within their QA specs and is not an issue. ********!
I've got an 07 suburban with the 5.3 I got it at 25k miles and it currently has 102k. The engine is significantly underpowered for such a large vehicle. I would go back and get the 2500 with the 6.0 if I could do it all over.
I know of several others who have the 5.3 and all say the same thing about burning oil and being underpowered.
I have had good luck with mine. I got a new 2500 in 6.0 for a company truck and the cam went down at 19k. It was under warranty, but still let me down. It sucked on mpg too.