BUT in my experience, people think they need part numbers 20X as often as they really do. If you think it's a dealer-only part (this one isn't), the dealer will sell it to you and look it up as part of their service. If you use Ebay or Amazon, a description is enough. And in this case, there are plenty of aftermarket gas struts out there at your local parts stores for a good price. Just go and they can punch in your vehicle description. In contrast to things like the serpentine belt where the parts stores data base has an error and they ask the wrong question before they decide on the length to give you.
Do you have a new need to have the part number I haven't thought of?
I used these: Amazon.com: StrongArm 4573 Chevrolet Trailblazer Liftgate Lift Support 2004-05, Pack of 1: Automotive
I replaced the OE units mid-2008. Still good today.
Even though listed for 04-05 they worked fine on the 03 Envoy. I do suggest measuring the fully opened length of your existing strut. If approx. 20 in. these should work.
I am assuming your inquiry relates to the rear hatch and not the smaller window in the hatch.
But as Roadie points out unless you have a need to only use OE replacements I'm very satisfied with these StrongArm units.