Keep putting him in his crib, and encouraging independent sleep. He is basically relearning how to fall asleep, since before the rocking induced sleep and the motion continued it. So, I would expect the 20.30 min naps.. but just continue to encourage the sleep in the crib. I wouldn't go back to the swing.. it will eliminate all the hard work you and him have done.
I would recommend doing Tracy's pu.pd strategy to encourage independent sleep. It's a middle of the road alternative to Ferber, Controlled Crying and CIO. Take a look at Tracy's new book, she has a chapter devoted to it, as well as the Pu.Pd board.
One last word of wisdom.. it takes time for teaching sleep.. it doesn't happen overnight. You have to stick with it, be consistent, routine oriented and not turn back to using a prop. It will be wonky, but it will get better and then you'll never have to worry about teachig sleep! It just takes time and patience on your part.
Hang in there and good luck!