Take a look at this
The trigger should slide of its own weight.
Take a look at the main spring (in the main spring housing). It may be "extra strong".
Look at the "left hand" leaf of the THREE LEAF SPRING.. It should be slightly arched.
Examine the SEAR/HAMMER engagement surfaces CLOSELY.
Is the hammer "stirrup" pin flush on both sides? Is the disconnector tunnel free of debris? Is the middle leaf of the THREE LEAF SPRING too "taut"?
Hope this helps.