Best Diesel to tow 12,000-13,000 lbs?

Thanx guys for all your comments. Wife & I bought a 34ft Big Horn last week and are now actively look for the right tow vehicle. Just drove a good-looking 3/4-ton 2006 Silverado with 166K mile on it, and it drove out pretty well. The dealer says he's might be able to get some maint records, but couldn't promise. My questions have to do with maintenance - ie., likelyhood of having to replace a big-ticket item like a turbo or a worn-out Allison. Should I consider getting an engine oil evaluation, and can the same be done with the tranny? Any idea what the average lifetime is on these turbos? Being really cautious here . .