I have the same exact issue. The issue could be the same as mine. If you have normal square blocks from Chevy, they are not angled. You need tapered rear blocks.
If you guys have factory block as a lift and you want to keep the factory blocks just order 2.5 degree shims. This will angle the rear diff so the pinion on the drive shaft is inline with the transmission. Chevy should have these included but it took me forever to figure out the issue
https://amzn.to/3pbzmdj
Throw these on your rear leaf springs and point the narrow end towards the front and the thick end towards the back. that should fix the issue.