Allysa, you said you were going to try a loong wind down. How did it go? if you put him to bed at 11:30 and he went off at 11:55 i'd say he didn't take that long to fall asleep (only 25 mins, when 20 mins is average for textbook kids). Of course, the goal here is that he's off within 5/10 mins but we have to take baby steps and go day by day.
Are you sure he's not in pain? hungry? hot? yesterday my lo woke up super upset (and early GRR) from his nap and he was sweating and very umconfortable. I had not noticed that is getting warmer and warmer and his room was like an oven when i walked in
We just have to persevere with the pd till he manages to lenghten his nap. I found that some kids get more wounded up with the walk in/walk out thing and you just have to remain there while the nap is restless and then when you're sure he's off, walk out. By reinforcing him that you'll be around when he needs it, he'll be less likely to wake up. But it's a gradual process with some setbacks. You'll make it, im sure, just take each day at a time.
Let me know if you notice any progress with the long wind down. Good luck!