A.M.
My son went through the same thing. I know you're going to think I'm crazy but the only thing that worked was putting him to bed earlier. He now goes to bed at 7pm and wakes up around 6:30 - 7:00am. The later he goes to bed, the earlier he wakes up. I put him to be 15 minutes earlier each night until I found the right combination (after trying to put him to bed later, change his nap schedules, etc.)
Hope this helps!