I purchased a used 2008 GMC 2500HD,48000kms 6 spd, 3.73 ext cab 4 years ago for 25000$. It now has 92000kms and really happy with the truck. The only items that I would change is the 4.10 ratio. Truck pulls great but it seems that it always between two gears at the speed I normally drive. If i drive 100 km/hr (62 mi/hr) it shift a lot between fourth and fifth gear. If I drive 110 km/hr (70 mi/hr) it work's great. But then my cruise control in the passenger seat start beeping;)
I will keep the truck for at least another 5-6 yrs and will refresh for retirement.
DanT