While I'm no fan of gmpartsdirect, I think all of the dealers (and yes, they are a dealer) are in the same boat: the parts supply is subject to ebb and flow and is usually beyond their control. Few dealers stock anything but the most basic parts and so parts can take two days to many weeks.
A few years ago when I needed a power steering pump there were zero in the country. Parts stores, dealers, etc. all told me the same thing: weeks to unknown. I was able to get a take-off from Brodie, thankfully. Now, they are easy to get.
Radiator foam insulation: took me six weeks recently from another online vendor. Reloader got his right away and he ordered just a few weeks before I did.
gmpartsdirect vs. gmpartshouse.com: direct tends to have lower listed prices and higher shipping; house tends to have higher listed prices and lower shipping. The net $ difference between the two is usually nominal and either one can come out ahead. One huge difference: gmpartshouse.com is a forum sponsor and Gene will go to great lengths to help you find the part and solution you need.
Finally, we're working on sponsorship for Zach's dealership and he's another good resource. I would suggest sending him a PM