Me too, I'd base it off his night rather than the nap. It's his A time that's the issue, he needs more to be tired enough to go down for his nap at a decent time. You could extend your time at the park, give him a bigger snack and then push lunch a tad later and then short wind down at 1:45/1:50 to be asleep by 2. The only issue is that you may have to cap the nap at this point, so bedtime isn't too late. But one step at a time :-)