Would it be worth buyng a used ECM to use with the programmers. Then when I take it to the dealer put my stock one back in??

Also what should a used one run me?

I don't know how much they cost. But I would hazard a guess that they are VIN locked to prevent that very thing.

I did that when I got EFILive. There's really no reason you couldn't do it for one of the "canned" programmers; If you got a new ECM and got it mated up to your truck with the VIN and proper programming, you could then use your programmer on that one and not touch your stock ECM with a programmer. Is it required? No. But if for some reason the programmer where to cook the ECM (not likely, but not impossible), you'd have a backup.

Will the dealer be able to see the predator even if I remove it before I take it in? I though I read somewhere on here that they could?

If you return it to stock, the dealer won't see it, but if for some reason GM wanted to investigate and dig deep (like a blown engine), supposedly with some REAL deep digging they could tell it's been done, but not with a Tech2.

How many miles are on your LLY's? I have to think 100k is just around the corner for a lot of us. If you're really worried about it, and you're knocking on 100k's door, just wait if you can. It would be hard if you only have 50-70k, but if you have 80-99k, I'd wait if you're that worried.