sandm is right.
The Napa, Autozone shock are typically Monroe generics and actually work well.
Rancho are always too stiff and don't last in salt conditions of the north.
Bilsteins are great the 4600 (yellow) are a good factory upgrade. The 5100 (silver) are mainly for lifted but you can get stock sizes. They like a little preload and will tow great but a little stiff when unloaded.
A rear sway bar would be a great upgrade to balance your towing better and help stabilize the rear putting less lateral stress on your rear shocks. It is not cheap but it was a big difference on my 1 ton.