Diesel,
The Duramax is one tough workhorse.
Maintenance is a breeze, just keep a clean fuel filter is the priority and you should have a good 250K+ mile engine with filter and oil changes.
And if your not satisfied with stock power (more then enough stock) add-on options are a plenty.
Just make sure the rest of the power train is able.
I would stick with the mated Allison trans, and at least the minimum AAM 14bolt rear end.
