Guess there are a few questions that could be asked/answered to help out.
Sticky? From the description the trigger won't return to the forward position after the sks is cocked? i.e. the rifle is fired or trigger pulled to release hammer (dry fired) and the trigger won't return without help.
Or sticky that as you squeeze the trigger it feels like you are trying to pull an elephant? If this is the case and after the shot you slowly release the trigger until you hear the sear reset and squeeze again it's nice and smooth, see the bit about the disconnector.
Can you re-create this stickiness if the TG is removed from the rifle? Most if not all the forces applied to the trigger are present whether or not the TG is installed. Only difference is the position of the disconnector when the bolt is locked down.
So I would look at the safety lever for interference. If the disconnector is worn, that is the tip that the bolt hits when in battery, the disconnector won't push the trigger bar down enough to properly engage the sear which will cause a heavy or gritty trigger when pulled as the bar scrap across the bottom of the rail the sear rides.
