Not quite third gen related but.... I have an 04 trailblazer that is a little too mush and bouncy for my tastes, i was looking into a set of bilsteins for it until i looked carefully and found it came with Bilsteins!! Question is, do the aftermarket versions differ from the OEM??

Bilstein is Bilstein...there is no difference

For that application- NO.

If you were to order shocks from Bilstein for that Blazer they would send you shocks with the same exact valving- that is not a sports car.

Now if you bought a performance shock from Bilstein with special valving to fit your requests, you would get a much better quality shock body and mounts, and the internals would be much better porting for damper movement. Its a whole different line of Bilsteins.

supposing i wanted to go directly to bilstein for a Custom damper, what would something like that cost, and who would i speak to about it? I don't want to hotrod the new truck but refining it to suit my needs would be nice. Would it be possible with the stock mounts or are we talking fabrication? I think the factory warrantee makes cutting and welding not very doable.

The make racing aluminum bodies take-a-part sevicable shocks that can be valved anywhere you want. They are made in all lengths and I am certain they have something that would bolt right in. Be prepared to spend about at least $400 per shock and the ability to tell the tech what valving you would require. He will probably just tell you don't bother with that type of vehicle becuase its kindof a crap shoot getting the valving to your liking.

Here, something like these-

http://www.bilstein.com/html/applications/sn/index.htm

Well, thanks for your time but thats way further than i'm willing to go. I'm going to check with Koni. If they on't make a direct replacement, i'll just live with it. Maybe in a few years i'll do somelowering springs and see what is available for dampers then.