[Thor]

With that much pressure it almost sounds like some type of metal rubbing, does the lever arm inside the sideplate move smoothly back and forth? Make sure the end of the trigger coil spring is pushed far enough inside the frame. Is the sear bar leaf spring overly strong? Does the sear bar rock back and forth easily in the receiver? Does it take a great deal of pressure to push in on the front of the sear bar with your thumb to release the firing pin (muzzle control and caution for empty chamber) Check this with the side plat off the gun. Just brain storming a bit. With the sideplate off, is it very hard to move the trigger in the frame? Just trying to isolate the problem. Trigger, sear bar, sear bar spring, trigger spring, etc
When adjusting the firing pin spring make sure you leave enough pressure to on that spring to keep the action open when the toggle knobs are lifted just starting the toggle sequence. The main spring is attempting to close the action but if you ease the toggle down they should stop when they start to compress the firing pin spring. If the main spring can overcome the firing pin when eased down the pin spring might be too light.
Oh another thing to check, is the sear bar leaf spring fully seated in its groove in the receiver? If not it might be binding the movement of the bar.