This forum has been awesome for the last ten years, helping keep my 98 V70XC on the road. I can't thank you all enough. The time has come... she blew a head gasket again due to the terrible EGR design and I just couldn't justify another rebuild.

I managed to snag an 05 Honda Pilot for a song and ...

All very good advice. Thanks!

Going even farther back (since I'm feeling a bit wistful ATM), Here's my now-16-year-old son sitting on the first Volvo in the family, a 240, awaiting the arrival of his B-day party guests:
And same son driving the now defunct V70:

Welp, it's time. The old girl has served me very well for over a decade but a clogged PCV return flow caused her to spit all of her oil out into the engine bay on the highway at 70 MPH, ultimately resulting in a blown head gasket.

I've already done the HG once and I ain't doing it again! On top of ...

Awesome. But I don't have a bluetooth-capable OBDII scanner.

Fair enough

MoVolvos, thanks for your feedback but I believe your description is inaccurate. Winter mode starts in 3rd gear, not "top" gear, which would be 4th. If I'm in 3rd on the highway and it's refusing to push into 4th there's no obvious reason W would push it into 4th.

That's what makes it so mysterious.

I've got my fingers crossed that someone will have some insight as to what the symptoms represent and why the winter mode switch makes it shift. That seems like a tasty clue to me...

MoVolvos, I used El Cheapo Wal-Mart brand. I figured that if I was throwing it away I didn't want to use expensive stuff.

Abscate, thanks for your speedy reply. I've been wondering if this might point toward solenoids, which you didn't mention.