Hey Jim, I found one with the first OS (12613248) that Ross posted up for a 2007 Classic:
2007 Chevy Silverado Classic 4.8 LR4 4L60E
What does the truck have in it now, is it a 4.8? If it's not, you'll either have to tweak this base file to suit the truck (VE, MAF, injectors, spark, transmission, ...) or get a factory-fresh file for it using SPS. I know for a while, some shops were selling base tunes where you pay a fee (was around $50 IIRC) and they'd use your VIN, flash a controller via SPS, read the file out and email it to you. I don't know if anyone is doing that still and I dont think I have a 1MB LS1 PCM lying around.