I start at CYVR with a PMDG 737 without any issues. Taxi to runway with 20-30 FPS.
This clearly proves the airport itself is fine and it's not the cause of low fps.
No issues with other FSDT airports.
You don't have any problem with CYVR too.
After takeoff things are okay until about 5 miles out at 3000-5000ft then FPS begin to stutter from 25-30 down to 3-5. eventually becoming a slide show. Usually headed east.
This clearly proves that whatever is causing your fps loss, is ANOTHER scenery, that comes into view ONLY when you are flying away from CYVR. So, CYVR is clearly not the issue.
Uninstalled and reinstalled CYVR 1.4. still falling FPS and then unflyable, never OOM though. Frustrated, in the past it seem to be solved by downloading newest addon manager but that didnt work. anybody having this issue.
By trying to act on CYVR or the Addon Manager, you are just wasting your time, because it's fairly obvious, from your report, the problem is something else, because you always noticed it when flying OUT of CYVR.
Try this simple test:
DISABLE CYVR in the Scenery Library, restart FSX and start a flight from the default CYVR under the same conditions, follow the same route, and see if you still have the same fps loss at 5 NM out.