Please post EXACTLY what you did (photo is helpful to show individual components).

Back when I did mine, I left out the Duralast PCV valve just to see, I HAD the same exact problem as you did, excessive vacuum causing hissing noise (air sucked into the crankcase via the RMS).
Installed the Duralast PCV Valve, problem solved.

So the Duralast PCV valve reduced the flow from 3/4" to 3/8" and somehow the 3/8" flow restriction does the magic trick, i.e., it is just about the correct amount of vacuum.

BTW, I am 20K since this mod, zero oil consumption. I recommend this mod.

Mine is exactly like the OP but possibly a different brand of valve. It is whatever carquest had for a 1998 k1500 replacement, which the duralast valve in the OP is..
I understand you suspicion of proper work, maybe I will make a youtube video but it's dark out..

It sings like a reed to the RPM..
Does sound like the RMS area or oilpan gasket or somewhere down there..

I sprayed my new connections with PB blaster to check for leaks and it made no difference..

50 miles or so now and still the same..

Mayo under the oilcap is gone already though and dry as a bone!

Spraying potential locations for a vacuum leak is always worth a try but it doesn't always work. In my experience, it is at best a 50-50 chance. A smoke test is a much better way to locate vacuum leaks. There are some Youtube vides detailing how to make your own.

VIDEO
https://youtu.be/VFNK7ltMRNU

What do you think of that?

When I did this procedure I used a different PCV valve and it did not work correctly. Got the correct one and all is fine. Gave my e39 to my son over a year ago. Practically no oil consumption. The car has over 175,000 miles with regular maintenance service.

Excess vacuum

Finally did the CCV delete
 

After resisting for years and going through quarts of oil, I finally got around to doing the mod posted here by BavarianE39. Thanks for the excellent detailed instructions.

I'm not sure how to adjust the size of the image here.
https://i.imgur.com/2rgm2CV.jpg

That looks real good. On mine I have the pvc valve tilted up slightly maybe 25 degrees, to let gravity help with the valve. Mine works like a charm. Great write up as noted.

951 miles since doing the ccv replacement and it seems there's no oil consumption so far. I'll post again when I've got more miles on it.

I've shared this ingenious repair to a couple of BMW drivers.