I'm going to tell you flat out, I don't believe you. If after all these years a G on the staff is all you can muster, you MUST find another teacher. What method(s) does he prescribe for you in general? If you've been trying all these shenanagans and still coming up dry, it tells me that you're not on any program, just the "let's give this a shot" program, and it's no wonder you're struggling. You must sit on a program and stay with it, otherwise you're doomed to your present limits. As a former teacher and a now current working semi-pro, surrounded by students and pros, I can tell you that what you say is ridiculous.
For example, I've never met a Gordon student who couldn't get to a high E or so after getting through six months of it. The book is right there in most every music store, most any trpt teacher knows it, and all know about it. Buy it and use it. Do exactly as it says. Don't mess around. Say, after a few weeks you don't like it. Tough. Stop the serpentine and stand there.
Can you, at the least, roll your chops in and blow out making the sound of a balloon leaking air at high frequency? Then your chops a capable of making the proper vibrations. Sorry to be harsh-- I rarely am-- but you remind of students I had back in the day claiming that they were doing everything under the sun and clearly were not. Proof is in the pudding. You seem a smart bloke with a goal in mind. Let's see you demonstrate that in the new year.