Just my .02. I traded my 03 LB7 for an early 07 with the LBZ. I couldn't be happier. It was well worth the extra money for how I use it. The fuel economy stock v stock was better on the 03. But 750$ later I was EFI live tuned and back in the 20's (with a lot more power
If you can at all afford an LBZ do it. You won't regret it. Not only do LB7s have injector problems, some of them have a starter problem where it grinds like every 10th start. I didn't find this out till after I owned one. 3 replacement starters didn't fix it, had to bite the bullet and get the 800$ dealer one.. If you do get an LB7 start it many times before you buy it.
And whatever year truck you get don't waste your money on a tuner or chip. Get EFI live. I got mine from Dan's Diesel Performance. He sent me everything I needed with the tunes exactly how I wanted with plenty of instructions a phone call away. Most reputable shops will do the same. EFI live isn't that much more expensive than a box tuner. And you can have it custom to how you want it. If you do a lot of towing the LBZ is a must. With EFI live you can use the turbo as an exhaust brake.
Hope this helps you. Good luck in your search!