You're probably going to have to wait longer than 6 months, but they should be out by the end of next year. Maybe september-ish. Usually when GM rolls out a new truck/SUV platform, the introduction order goes:
1. SUV's
2. light duty trucks
3. HD trucks
I would definitely wait for the new ones. I wouldnt hesitate buying one right away either. On the K2XX HD trucks, the drivetrain and chassis is just going to be a carryover from the 2011+ trucks. So its not like theres going to be any "bugs to work out". Because really the body/interior is going to be the only new part on the HD trucks.