The autos in trucks 10 years ago were not as strong and good as they are today. I chose a 5 speed manual, no regrets, just depends if you can drive a manual.
I have had manuals in my auto inventory most of my life, you really need to be comfortable driving one before deciding to tow with one.
You need to be sure you have enough clutch to handle the torque that a diesel puts out. I upgraded to a Double Disk and have had no issues pulling 11,000# up 6% and 7% grades at speed.
Mine is a daily driver, so shifting is second nature.
