2000 Nissan Sentra-spark plugs are hard to remove-and go bad quickly-Also rough idle & intermittent miss

I'd like to know if I can do anything to make my spark plugs easy to remove and replace, and why they are always hard to remove--and why some of them went bad after less than 2k, when they're rated for 100k miles.

It's a 2000 Sentra XE with the 1.8L with California emissions, and the Auto Trans. The car was made during the 1st year of that body style, but it wasn't the 1st year of the 16 valve, DOHC 1.8 engine, which has an iron block, aluminum head, and a steel timing chain. It has 190k miles, but has been to the dealer for all the factory recalls.

These new NGK Iridium plugs are from Auto Zone, don't appear to be counterfeits, and are still hard to get screwed in all the way, in cylinders 1 & 4, even after I soaked them for 3 days in PB Blaster penetrating oil to get the old ones out, working them back and forth about a thousand times. And then I used a new thread chaser, spray cleaner, & anti-seize on the plug's threads. The thread chaser was hard to get all the way in the first time, but went in much easier the second time.

After all the trouble I had with the spark plugs 2 years ago, I started checking and/or changing them every year--at less than 2k miles per year (which also means I only need to change the full synthetic oil once a year, along with a high quality filter from NAPA). But the plugs are still being very difficult again, one year later.

Also, I've been having issues off and on for the last few years with missing, intermittent stalling, & intermittent missing--like it has no engine power at all for a few seconds, then starts running OK again. And it idles rough, so I'm thinking maybe the timing chain is stretched, which is known for causing rough idle.

All the plugs had some carbon build up @ 2k miles, so I'm trying to get them changed again this year. Been working a whole week on those last 2 plugs, trying to get them to screw in as easily as a new plug should--and to screw in all the way, like #2 and #3 did this year. 1 & 4 are very hard to get started, and hard to turn. So I'm taking my time, and hoping I can get them to screw in all the way, eventually, some time this month.

A few years ago I had to change the ECM, all 4 coil packs, some sensors, the radiator & thermostat, and the spark plugs. And the only ECM I could find was used, on eBay, so I don't know if that's 100% good or not.

The 2 cats were changed 5 years ago, but the code for the cats came back after one of the coils went bad. I suspect the few miles I drove with a bad coil contaminated the converters, and a can of cat cleaner didn't fix that.

So not sure why it runs fine for months, then starts missing again, intermittently...

I know it's getting kind of high in miles, but it is rust free, and I was hoping for a few more years before getting a reman engine, or a better car, i.e. a V6 Toyota Rav4 (used, obviously, since they don't make those any more), some day.