Update: It was the Fuel Pump Relay!
So I checked and I had last replaced the relay with a crappy KAE one. I should have realized that right away. Volvo one is the way to go with that relay always!

When it happens on the hwy is when I'm just cruising at very part throttle.

If they weren't gapped right then I'd have issues when getting into boost. It would start breaking up.

I gapped them when I swapped them out about 4 months ago.

No CEL, Bosch & NGK cap/rotor/plugs, ECT is a Volvo.

I'll check the ECT wiring and the MAF connector!

Good point on the relay. I thought I got a Volvo one, but I'll look. I might make a jumper and use that to test when the engine's hot. I just got a fuel filter that I was going to throw in there. The MAF is original so that could be it. How long do MAF's last before failure?

Background: 337k miles on her, new clutch & new turbo in the past 5 months, all new vacuum lines, plugs & wires & cap/rotor replaced in the past 8 months, very recently a new purge valve & new ECT & new thermostat trying to solve the problem. Symptoms: After driving for an hour o...

Thank you so much! Without your pictures I would still be searching for that darn fuel pressure regulator line.

As an owner of a 1998 V70 T5M I got really excited when I found out that a short shifter kit was available. My only previous experience with using a short throw shifter is in my old Altima. The stock throws on that one were so long I'd accidentally change the radio station when shifting into 3rd so ...

Eeked out one more mpg (up to 22) on this last tank taking it a bit easier on the boost. I can't help but dig into it every now and then. I think I'm going to add a boost gauge just so I can have more of a visual on what the turbos doing. Any thoughts or advice on putting one in?