Ok, I've thought about this some more. With the trigger installed, if it's pulling the bolt down even after it's been cocked... That's a timing issue of the trigger sear that catches the bolts sear. The issue with it being hard to lift at all times... May not necessarily be a timing issue. Ok. Once again. If the bolt cycles fine with no resistance when the firing pin & spring is removed, then your heavy bolt lift is coming solely from the cocking & spring compressing motion. It has to be something to do with: the spring weight itself, the surface & condition of the cut at the rear of the bolt that cams the spring & firing pin into cocked position or the bolt shroud assembly at the rear of the bolt( shroud threads included). Could it be that the bolt shroud & firing pin assembly is screwed one turn into the bolt too far? I've never saw this to be possible, but you have a problem and it's a possibility.