Rock Auto has new GM units with a lifetime warranty for $290. https://www.rockauto.com/en/moreinfo.php?pk=7179908&cc=1433415&pt=7556&jsn=485
I installed these a couple of years ago on both of my XL Denalis and I tow a 7500 lb camper. They're good as new. I also installed the Dorman compressor on my '07 which is a good unit.
have you ever checked to see what kinda pressure you're seeing while towing that big camper?
I searched around before my first trip and posts I found had me not wanting to go to high