First your going to need a 35 series of truck for the payload. The newer (2011- present) SRW as stated can handle about 3500 lbs but 3000 is where I personally draw the line for DRW's.
If your looking at used diesel powered the 2003-2007 Rams and GM twins cost roughly 25-30k depending on mileage, condition. These were in general good years for the engine's mostly cause they didn't require the heavy emissions that were put into effect as of 2007.5. All three had issues in the learning years with the new emissions systems. I myself would avoid those years (2008-2010). Since 2011 the Ford and GM started using DEF which really helped with emissions and they seem to be doing much better. Ram started using it in 2013 with good results also. Any 2011- present trucks are nice and I wouldn't cross any off the list.
Of course if you have $60k all of the new trucks are great. Ram even has a new air suspension in the rear to make the unloaded ride smoother.
Good Luck