Hi Mike ! I too have used excessive mouthpiece pressure in my youth. I play trumpet, btw. (I did not play from 1985-2012) I’ve been dabbling with Greg’s method for a (long) while but I’m really digging in now and seeing benefits. I have found two things that have helped with excessive mp pressure.

1) playing the leadpipe. Sometimes when I have a spare ten minutes I will do the warm-up through lead pipe work. What i mean is Body’s Concert Hall breaths, ahh-ooh, add air, use tissue, add vizualizer, blow air through mp, then some time on the leadpipe. Getting a sound on the pipe is So Easy ! I keep reminding myself that I can play with ease.
Greg says you can get a horn leadpipe…do it. 🙂
1a) My brain really fights doing that list above…Body’s Concert Hall etc. Over time, i have many times, slowly gotten away from doing those all-important things–in order to get to what my brain thinks is Real Practicing. I have finally caught on to this. Now I do BCH breaths and humming whenever i can. It Is Working!

2) bringing the magnifying glass to the mouthpiece pressure. When I paid attention to it, I noticed that my left arm was the one doing the pulling of the horn towards my face. The first thing i did was to push it away with my right! (eye roll). Now I am consciously working on just Not pulling in with my left arm. I have eliminated some pressure already…the tendency is to pull in more as I go higher so I just experiment with Not Doing That. I have to really Pay Attention.

I hope this helps!
Cheers,
Chris