3 thoughts - with all of the changes you have made (putting to bed earlier and later...), have you given sufficient time to let him get used to the change? Two weeks at least?
I have also heard this - if he wakes up consistently around the same time every day, go in 10 or 15 minutes before he would wake up and wake him slightly. Let him fall back asleep (or get him back to sleep). This should make him go through another sleep cycle (45 minutes to an hour). If you do this for a few days, he should begin sleeping through that wake cycle.
Our furnace is set to get the house a few degrees warmer at 6:30 am, but starts to cycle around 5:30. I wake up around 5:45 getting hot and start kicking off the covers - could this be happening to you?
Good luck - I have 2 non-sleepers and it's rough!