:( Starting problems.
Started having problems with engine starting - Clicking noise from starter area when turning key on and off to start. Towed to the dealer today to determine problem. Battreries seemed to be good.

2004 GMC 2500HD Ext. Cab Long Box ; Duramax (LB7)/Allison; GMC bed liner; Air Lift Super Duty air bags; Michelin LT265/75-R16 LTX M/S ; Luverne Running boards; Bilsteinshocks; Isspro gauges; Racor frame mount fuel pre-filter.

Loose connections on the starter

Read your post this evening, then grabbed a flashlight and headed for the garage. Been having the same problem for a couple of months now on my 03 Duramax, only it has never completely failed to start. It usually clicks a few times, then starts, and then the problem goes away for a few days.
Sure enough, the battery cable connection at the starter was loose. I could see where it had been arcing, but it tightened up okay.
Thanks for the post.