J.S.
I can't say anything about the CIO method as it never worked for my son. I know when my son was 16 months I tried my hardest to get him down to one nap and it only made things worse as far as him sleeping... so I stopped and kept him at 2 naps. All of a sudden at 18 months he did it himself. He just wouldn't go down for his morning nap but was tired around noon. That's how it has been for the last 3 months.
Unfortunately our children aren't made to fit to our schedules. Part of being a parent is being sleep deprived... not what you wanted to hear, I know. I never wanted to hear that either... I just wanted solutions.
Personally, all I think you can do is try to replicate his bed time routine night after night...consistency. Secondly, watch out for how much motrin you give... and how often and for how long... it does have some nasty side effects.
What also worked for my son... because he was also a super early riser (5am) was to move his bedtime to later... very gradually... by about 20 minutes a night. I know that there are some die hard fans of Healthy Sleep Habits book, but it does NOT work for all kids... my son is one of them. I was putting him down at 6:30 at night successfully, but he would wake anywhere from 4-10 times a night... so I talked to my friend and she said to move his bed time later... it was rough the first couple weeks, but now he is perfectly fine... he only wakes 2 times a night which is fine with me. I can deal with that... but NOT 10 times!!!!
Hang in there!