If you're checking pH and it's from 5.1 to 5.3, I don't see where the problem is, unless you're only looking at the mash and not the sparge, but with batch sparge... gosh, I really don't see the problem.
That being said, my own process is very close to your second option:
"Strike with 4.25gal (about 1.8q/lb), add about 1gal of 190deg water to MT (top off/mashout?), then get about 4gal 1st runnings, and sparge with 4 gal to get total pre boil volume?"
I have always mashed at a ratio between 0.8-1.8 qt/lb, almost always add an infusion of some amount of boiling water to get half the boil volume out of the first runnings, then sparge with half the boil volume. Works for me.
I suppose it's possible that by skipping the infusion and mashing and sparging "thin", you were extracting more tannins than I would. But I really question this, if you know your mash pH was okay, and I would think the "okayness" of the pH would carry to the sparge when batch sparging. But I could be wrong. Maybe there is an impact, and the infusion really does protect against this.
I'm not going to say I've never experienced astringency in my own beers. I have, a few times, but it is typically very slight. Probably due to pH problems, also could be because I grind my grains so dang fine, down to flour. But I can handle a slight astringency on rare occasion. Nobody's perfect, 'cept maybe Jamil & Gordon & Denny, right?! Maybe you just had one of those days. There are a lot of variables, and we can't all be perfect all the time.