Roy I haven't replaced a turbo yet (at work) due to a failure from heat. (actually I have only changed one once due to a mis-diagnosis by someone else, lol) I think that is crazy considering how many "over programmed" DMaxes are out there.
I have an 05 Duramax, Hypertech on level 2, AFE intake, and Banks cat back exhaust. I leave mine on level 2 no matter what, whether I am driving to work or towing the hauler. I tow my 34 ft toyhauler (probably 13000-14000 lbs loaded) by the pyro. I can bury the needle past 1600 if I wanted to. (but I never do) Once my my EGT's reach around 1400/1450 degrees on the big grades then I back out and keep them from going higher and it still pulls good. I usually keep them there and haven't had any problems at all. Many diesel guys have told me that 1400-1450 is just fine especially for semi short periods of time. I had some guy even tell me on dieselplace.com that he has run 1400+ degrees for 15 minutes straight with no problems. I wouldn't push it that high for that LONG, but you are safe below 1450 in shorter spurts. You gotta remember turbo temps are gonna be a couple hundred degrees LOWER than your manifold temp. Also: Hope that helps.