I had a similar problem on my new RH .45 Colt/ACP. I have a good friend who is very savvy with Ruger revolvers clean it up. Problem soon returned, worked on, and so on. Eventually it got to the point that the entire trigger system just "locked up" and the trigger would stop about half-way back. I had to send it back to Ruger (unfired!); they didn't send a report of what work was performed, but I believe they replaced the entire trigger assembly (it looks like it fits better than it did previously). I haven't had a problem since.
My advice - Let Ruger fix the problem. THEN spend time on a trigger job. It would be a waste to spend hours polishing a turd, just to have Ruger replace it, then do it again.