Edit - additional info
I created a video of me trying to re-create the tone and intonation problems that you have and I think I succeeded:
Then I changed to my normal setup and embouchure and recorded a little more:
If you're not familiar with strobe tuners, when the blue bars on the screen ...
Even if you are "out in the boonies," I strongly recommend getting an expert to evaluate your axe. This may entail mailing it off to some clarinet repairman and waiting for him to return it with a report, but that's the best way to determine for sure whether it's the instrument or your technique that is at fault.
By the way, are you absolutely 100%...
With an instrument that is consistently playing flat, the first thing to try would be a new barrel. Your 66mm barrel is the standard, but you can easily find a 65mm or 64mm to try. The shorter barrel will shorten the instrument and make it play sharper.
The first thing to try is playing another clarinet. If that's flat as well, it's you. If not, start looking for mechanical solutions. But it seems unlikely that what seems to be a standard, reasonable quality instrument would be 'built flat'.
Try smiling a little more while you are playing. The warmer your instrument gets the sharper it will be, blow warm air into it before you play. Blow more air into you instrument, even if you are playing quietly.