Do you have spring tension on the disconnector (trigger bar)? Its spring is also the trigger spring. If things are OK there, check the sear spring for correct installation.
I do NOT recommend disassembly of that gun for routine cleaning beyond removing the bolt. I remove crud from the receiver by hosing it down with Gunk Out or something similar then a dose of G96 Gun Treatment. The idea that one must tear down a gun into its tiniest parts and clean each part to surgical standards is ridiculous. (Yes, Marines, I know about the old Gunny, but he isn't with you now and there will be no inspection in the morning!)