the '07 Duramax is one of the best tow trucks ever built. Reliable, economical and capable. I doubt if any new one (cough-DEF, cough-fuel mileage, cough-complexity) will be any better for all 3 measures.
It's a real classic. You might just keep a maintenance kitty $$ and save the difference for a new truck. But worse case, repair costs would still be less than a new truck. The only downside is failure on the road and driving a dated truck. Probably the deciding factor is to have a reputable mechanic to keep it going before something bad happens.
