FWIW, I have replaced the stock shocks on my last 2 trucks with Bilsteins. They are a huge improvement. On my current 2011 Chev 3500 I replaced the rear shocks at less than 10000 miles... and also added Timbrens at that time. I found a huge improvement. I just replaced the fronts this week with Bilsteins at 20000 miles. Have not towed yet, but at 20000 miles they were toast. Now, I do have a plow that I use in the winter, but don't leave on when not plowing.
The bottom line is that your shocks are well past needing to be replaced. You will have a much better towing experience when you change them out.
Best...Irish
