The truck your looking for would be a good choice. I wrench on vehicles the 350 vortec was one of the best engines GM has made. That being said the New LS engines cannot be beaten. The 6.0 is a absolute powerhouse. They are still largely based on the traditional small block. Being pushrod engine. The worst thing I've even had to do to one was head gaskets and being a pushrod engine. even that job was a sinch. About the worse expirence you'll have is feeding it, and the rearest exhaust manifold bolts break the heads off. They make repairs for those too.
The new diesel engines perform like never before. We just did a egr and dpf delete and put a tuner in a new f250 6.7 that was 150 horse capable. It makes a rockeship out of a 3/4ton truck. But im here to tell you, you don't want the repair bills, bc you WILL have them. Thanks to the EPA those engines are so choked with emissions devices it unreal. The fuel systems are so picky, like the 6.4 powerstroke, once the fuel system is contaminated, it all has to go. Tank and lift lines flushed all new injectors, feed lines, injection pump. Bc the pump will chew itself up and send metal all through the fuel system.7500$ worth in just fuel system repair.There nothing like the old diesels. Even the mighty Cummins the new 6.7 wastes a turbo and it will, your out 3600$ Duramax is no exception. I personally had the whole cab off the frame on a 12' model putting in a used engine. And the used engine was 5,000$
You can buy alot of gas with all the money you'll save. I'll try and find the pics I took of the cab off Duramax. That was the most intrusive job I've ever done.
As a current automotive technician, having to do these the of insane expensive intrusive repairs is why I drive a 69c20 with 250ci inline 6cyl. Simple yet effective.