Kim,
Could you try putting him down at 3 and waking him at 4:30 so he's still tired for bedtime?
Is he still sleeping through the night?
It is very possible he could be ready to drop the nap. If you were to go that route, I would still have quiet time in his room, perhaps for an hour. In this case, he may fall alseep anyway, and maybe nap every other day. Does that make sense?
HTH