M.S.
A couple of thoughts:
How many naps is he taking right now? If he's still on 3, maybe he's ready to go down to 2 naps a day?
Have you experimented with his bedtime/naptime? Maybe putting him down earlier so he's not so over-tired or putting him down a little bit later so he IS tired enough to go to sleep (everyone said the former works best for babies, but the latter works better for my daughter).
Finally, it may be worth just sticking to one method. If you're going to let him cry it out or do gradual extension, then you have to stick with it for a bit until they learn to fall back asleep on their own, or else they get the message that if they cry harder, then you'll eventually come. I'm not saying that letting him cry is the best option for you, it may or may not be, but if you do choose to do it, then stick to it so he gets a consistent message.
Good luck! Hopefully it's just a short phase!