Blowby is stuck or bad rings (or possibly the PCV system
I wish I had known as you were tracking up I-29, I would have helped around KC.
What kind of spark plugs did you put in and what kind of plug wires did you use?
The proactive thing you can do is to buy a can of Seafoam from an auto parts store and dump 1/3 of a can into your oil. Drive it for a short while - I'm not sure what a short while is and the instructions on the can are silent. I would guess 100 miles or so would do it. Then change your oil and filter. The bummer is that in Montana I doubt you can find a Mann filter unless there is a local Volvo dealer. I have heard the NAPA gold filters are OK but I have never used one. Even if you wound up with a FRAM it will just mean clacking on startup until you can find a real filter.
It may or may not help but it can't really hurt anything.
JRL had great results after seafoaming his oil on compression. Good compression means less blowby. Hopefully Jim will jump in on how long to run the car with the Seafoam before the oil change.
You didn't say if you have a turbo or not. Particularly with a turbo, check all of the vacuum lines and the intercooler lines. The vacuum lines break / crack and the intercooler lines tend to just collapse under revs when they go south.
Is your check engine light on - if so get the codes read and post them back. The codes give us a lot to work with.
I'm glad you escaped Gus and clearly you were nowhere coastal for Ike.
A link to great pictures from Ike:
Ike Pictures - #11 is amazing