2002 STS - Bad misfire, then just disappeared.

So., about a month ago I'm driving to Denver. About half way (200 miles) I notice the engine missing as I try to accelerate up a hill at about 70 mph. Then it runs fine until I get to Denver. When I stop I notice it's missing pretty noticeably when idling in Drive, but not in Park.
The next day driving around it is missing pretty badly accelerating from a stop. SES light blinking intermittently.

I try to hammer it hard a few times to smooth it out. Seemed to go away as speed built up.
Then after driving another 30 miles or so on the highway, the symptoms just disappear. Ran fine on the trip home, running fine now. No sign of any misfire.

Didn't pull codes as I figured I'd just get P0300 in history.

What does this sound like? Clogged injector that managed to unclog itself? I have run Techron through it., but several tanks ago.

I have noticed a hairline crack in both my coil cassettes, I expect to have to replace them soon, but if this was causing the misfire would it likely be intermittent and then just disappear?
I know there are a whole slew of things that could cause a misfire, but how many would be intermittent and then just vanish?

TB is clean, FPR is nearly new. About 69,000 miles now.
May be time for new cassettes, plugs and boots.