Okay, after spending some time to analyze the now removed Procede fuel pressure sensor connector, I have now realized the problem.
So I am posting these pictures here partly to prove that I am not a complete idiot who spent four consecutive days trying to remove a simple connector but also so I can share the lesson I have learned from this experience.
The Procede and OEM fuel pressure sensor connector is exactly the same with one major difference. The Procede connector has an additional gray tab, which is supposed to make pressing down on the thin black release tab easier. This gray tab is completely independent of the rest of the connector and moves around semi freely and it is supposed to sit flush with the back end thin black release tab.
This is what it is supposed to look like from the front end of the connector. Pressing down on the back end of the gray tab is supposed to push down the thin black tab and push up both pieces on the front end to release the clip. Notice how the gray tab is sitting further in than the thin black release tab, this allows the two to be raised upwards in the front when pressed down in the back.
This is how mine looked like when I removed it. Notice how the gray tab is pushed forward more and it is almost flush with the front end of the thin black release tab. Also notice how the gray tab is already touching the edge of the locking mechanism leaving it no room to move. Therefore, pressing down on the back end does not raise the front end and it was permanently locked.
Not sure if you can tell by the pictures but the only reason I got it out was because I got under the engine cover with a screwdriver and forced it out and broke the top part of that locking mechanism and that was the only way I could get it out. If I were to reinstall it, it might just remove that gray tab altogether. My theory is that during installation, I must have pushed forward on the gray tab when installing the connector and that must have jammed that locking mechanism. So be careful not to make my mistake and push only on the connector itself, not the gray tab.
Live and learn... cost me for days of my life and cramped, cut and bloodied hands but I will never forget this lesson...