1) How difficult is it to install lowering blocks on a 08' silverado with a trailer hitch?
2) What is the best hand held programmer for the 5.3?

 

I think the stock blocks on the new silverados are 1 1/2 inches so if you just want to level the back with the front then take that block out. it's not hard. 4 nuts for each block. and instead of a programmer(from experience they ain't that good) get a blackbear custom tune. helps out a lot. but if you're dead set on a handheld, I hear diablosport makes a pretty good one

 

i have an '01, so i'm unaware if they put blocks in the new model trucks to raise them, but do what country09 says and take them out to lower it. if your truck doesn't have blocks, just get lowering shackles. or lowering hangers or leaf springs (more expensive).
i have the 5.3L and installed the superchips flashpaq. i'm not going to argue it's the best out there, but i'm very pleased with it.