Just some checks: With the slide off, just lift the right side trigger bar with your finger tip VERY lightly as you press the trigger. If it drops the hammer, the spring is the problem.
Is the trigger bar spring screw loose (same screw holds the mag release spring).?
Just check it by using a common screwdriver "that fits the slot on the screw" by tightening it slightly and see if the screw turns. It shouldn't, because it's staked in place just snug against the two springs. If overtightened it will distort a spring arm on the trigger bar spring.