Glad it finally worked out for you. Nothing as satisfying as the successful conclusion of a quest.
So, maybe I've just been lucky? I have Vollrath half sheets, and Nordicware quarter sheets, and, at temps up to 500F, have never had one warp. None of mine came with snap-on lids, though. Sounds like a valuable feature.
A couple of comments regarding issues raised in this thread.
Rolled or wire edges certainly contribute to warplessness. Basically, they stiffen the pan and give it backbone. Gauge is important, yes. But I think the rolled edges are equally so.
Quarter sheets are probably the next best thing to useless in a commercial kitchen. But at home I find them incredibly useful, for all sorts of tasks. I use them as prep platters, cook in them, carry foods back and forth from the kitchen to the outside grill, drain fried foods on them (when fitted with a rack) etc. I've got a half dozen of them now, and will likely increase that number. They're also a whole lot less cumbersome to wash in a home sink than the larger models.
Despite what somebody said, full sheets will not fit in all home ovens. They'll work fine in a 36", but will not fit in a 30" stove. The latter being far more common, it's why half-sheets make the most sense.