I have towed with 2 Duramax trucks, and loved them both. Both rear-end gears were 3.73.
The major difference is the transmisson in the '12 is a six speed. That brings the cruise RPM down to around 1800 at 70 mph.
I do hate the DEF issue, but I guess the folks at the EPA like having all the air scrubbers driving around. So we can have more iceburgs, of course.
Jeff & Cindy
'09 27FB Flying Cloud
'91 350 LE MH