Hey Robin: For whatever reason I never had an issue with Zach, I think because he likes sleep so much and we made it a HUGE deal that he got a big boy bed.
Do you shut his door at night? I have a friend that her son is a lot like yours. Very active, spirited. Well she had a had time with the transition, but bascially she made sure his room was compelety child proof, had safe toys in there, a night light and once she put him to bed, she shut the door and DID NOT GO BACK.
She is not a Baby Whisperer follower, so if he cried, she let him cry (unless it was really bad) and also she has a video monitor in there so she can she what he is doing.
He may just need time to adjust and now that he has the freedom to get up whenever, he may do that at first.
I know with her son, he would get up as soon as she put him down and play for like an hour before going to bed.
You may want to try the bedtime chart I did with timer. On your chart, you could always put the last thing you do is BED, Story and then set the timer for say 10 minutes for Mommy to stay, but when it goes off, Mommy leaves. It took us 3 days and that was it for the timer and chart to work, he know longer throws a fit at all.
i hope this helps some.