I am in need of a newer rig!

I transport horses and I currently have a 2009 2500 Cummins. She is wonderful minus..... I have a bad back, and the seat is uncomfortable, I am having shoulder issues so I am switching arms while driving constantly. She has had a few issues since I bought it last year in May. I purchased it from a local dealer with 70K miles on it and now it has 146K. So, I drive quite a bit and I tow a three horse trailer around the west coast. I am looking for comfort, and reliability...

Help! What do you consider the best years and why?

Thanks!!

 

my dad had an 08 3500 Mega Cab...it was one of the nicest trucks ive ever been in aside from my buddy's 15 3500 LTZ Silverado HD...but that's a much newer and nicer truck still.