The cucv vacuum valve does vary the vacuum depending on throttle position.
I know they are not easy to find but I recently won a lot of 50 of them, brand new AC Delco part number 14057219. I believe these were manufactured in 2008.
I will have them here in a week or so(they were picked up today), and they will be for sale in the classifieds.
I will also include a copy of the TM instructions on how to change and properly adjust it. There is a special tool that is called out in the TM, for setting it correctly, I plan to include a homemade wooden block that can be used to properly adjust it, also.
If you want one, PM me for details until I get an ad listed(after I get them in my possession).