By now ya'll have probably heard about the SEMA Silverado with a 427(LS7) but thought that I'd throw in this form GMinsideNews:

Chevrolet Silverado: In the 2008 model year a new SS version of the Silverado will come out. It is said to look very aggressive and sport a 500+ HP Small Block V8. A two-mode hybrid Silverado will arrive in January 2008 as well. There is also speculation about GM adding a 7.5L V10 powertrain to the HD trucks to replace the 8.1L Big-Block V8.

I hope they know something we dont!!!

I may be the first to attempt a 7.5 rcsb conversion(from Cadillac)

GM is working on a 7.5L DOHC V12 powertrain that Caddy will likely use. There is also a Turbocharged version of the V12 in the works.