Diesel repairs are very expensive. A new set of injectors costs more than a complete engine rebuild on a gas engine. The pre-2010 diesel pickups as a whole had lots of reliability problems. I would look for a 2010 pickup from any of the three companies over almost any of the older trucks. One possible exception is the Chevy 2006-2007.5 (Classic) trucks which had an unusually trouble free engine.
A friend bought a 2002 Chevy diesel earlier this year with 120K miles on it. It had recently had the fuel injectors replaced at a cost of $4500 so it was a good buy. Had he bought the truck for the $22,000 he paid and then later had to spend another $4500 on the new injectors it would have not been a good deal at all.
Lots of diesel forums that are easy to find and a very few sources of repairs information that is much more difficult to find. Appreciate that with 20,000 trucks sold of a particular engine model and year that probably 10,000 of the owners sold their trucks before the trucks needed to repaired and so they will speak in glowing terms about how great the truck was. There are both owner repair surveys and ones done of repair shops that cover the different makes and model years and none of the big three look good for the 2001-2009 years as a whole.
I found when I looked for a used diesel pickup with less than 60K on the odometer in 2011 that all the ones for sale were priced at over $35K as their owners had paid much to much for them when new. I ended up spending $42K and getting a brand new GM Duramax truck instead with the full warranty.