Kathryn, all the comments so far have been good except that the factory probably told you to try them before the first time you sent it in, right? If not, try 'em. For the record, I bought a Mk1 in November that wouldn't go through 5 rounds without jamming. I did the following:
1. Switched to Winchester "Dynapoints" from Kmart. I know, I know, but they work. one of my magazines now occasionally got through all 9 rounds. This is apparently not your problem.
2. Cleaned the gun thoroughly. Had previously done this but had over-oiled. Most of my other guns are shotguns which apparently are less sensitive since they're so much more powerful. With less oil, the gun cycled noticeably better and the stovepipes and other ejection problems ceased.
3. Played with the lips on all the magazines. This took me what would amount to about an hour of messing with the mags. I used a pair of pliers and kept a box of magazines (the paper type) next to me in dad's shop to function fire as I went along (dad has had the box for years.) This helped a great deal since I could test it immediately but didn't have to work at the range, but depends on how well insulated your house is.
Now, I haven't had a malfunction since. Couldn't be happier with it, except that one magazine goes in tight and sticks in the gun. Come to think of it, I'm going to ask about that.
Hope this helped a little bit. Maybe you should also check out
http://www.rugerforums.com and see what they have to say over there. Good luck. Also might want to point Ruger to this thread if you think they'll look?