I “came off of” Steel Government Model 1911s and they mask a lot of poor technique ...
I would suggest that "steel" doesn't mask anything. If its not an issue shooting a steel 1911 then it isn't poor technique
for that gun.
All recoil operated semi automatics require something to recoil against. Generally this the mass of the gun, and the shooter's grip. Some guns seem to work ok without a firm grip. Some do not. Sometimes its fairly constant across a model, sometimes its unique to an individual gun.
From what is described, other polymer frame pistols work ok for you. Other GLOCKS work ok for you. You've shot the same model Glock at rental and had the same problem yours does.
And the Glock that give you issues works ok when other people shoot it..
(have it got this right? )
All semi autos are a balancing act. The are designed to operate within a fairly narrow range of conditions. Some guns operating range is larger than others. It seems that you have found a certain model Glock with a preferred operating range where your usual grip is borderline.
You can try different springs, see if a lighter or heavier recoil spring changes your results. It might, but it might not. I can't say, I've shot several, but don't own any "combat Tupperware". I don't do Glocks, don't like them. Personal thing, doesn't apply to you...
I used to think their slogan "Glock Perfection" was just advertising hubris. Distasteful, but irrelevant. Now, I'm wondering if that slogan isn't actually referring to the need for the shooter to be "perfect" in order for them to work. (Perfect being what ever grip is needed to have the pistol function properly)
I understand the frustration, when you are doing what seems right, and what works fine for all your other guns, but one gun (or one specifc model) chokes when you shoot it, and someone else, doing what appears to be the same thing you do has the same gun run like a sewing machine.
Its not just you. Its not just the gun. It is a specific and unique combination of factors of you AND the gun, together.
I don't think anyone can tell you how to fix things over the internet. Not sure we could even watching you shoot. All we can do is suggest things that MIGHT make a difference. What actually fixes your problem might only be discovered by trial and error.
Good Luck.
Oh, one thing I can tell you, if you are looking to get the most from selling a gun, do not sell it to a store, pawnshop, or dealer. Generally they will only give you about half of what its worth, or less. If you need some money NOW, and can accept the loss, fine. If you want to get closer to full value, don't sell it TO them, sell it THROUGH them, on consignment. It will take longer to get your money and they will still take a bite (maybe as much as 15% or so, depends on the dealer) but you'll get more than selling it TO them.
Best value is usually obtained by selling the used gun privately, then going through an FFL dealer(s) (and paying their fees) for the actual transfer as the law requires.