I just put Bilstein 5100's on my Dmax, what a difference it's made!!! Tightened up the whole feel of the truck.
FWIW the prices in that link are pretty close to what I paid out of the states.
I second that. I just put new shocks on my '06 Duramax in June and went with KYB Monomax on advice from someone who felt they were better for our application. Wished I would have went with the Bilsteins.
I have am 2001 and i pull a 31 ft fifth wheel and for the ride improvement and handling improvement i will also go with Bilsteins, they have always seemed to be the best.
used Rancho 9000's on my GMC Dually, they have 9 adjustable settings, run them on 9 with the truck camper and sled trailer on, holding up very well.
For your truck maybe the 5000's would be good enough.