I have a 2005 GMC 2500 duramax and I tow a new 303RLS reflection (just got it) You can see the pic in my profile (excuse the salt on the truck) and it is with my winter tires 245/16's on the truck....
Another vote for the Bilstein 5100's here. I'm on my 3rd Silverado and have replaced OEM's with Bilstein on all 3. I can't speak for Ford or Dodge, but they are a huge improvement over GM's shocks.