My ds manages well 13 h max without a nap. But, on the other hand, we usually do set bt, so we put him to bed at the same time regardless of the routine. I think that it usually helps him adjusting his body clock. So, if you would like to implement a set bt at 8 pm, I would try to be consistent with it (I usually make it plus minus half an hour) for several weeks and he could adjust to this. Hopefully, he will continue to sttn, that is a fantastic progress.
Btw, for the grumpiness, I found that after 3 yo the misbehavior is often caused by other reasons (being 3 is a good reason
) and we had 2 months of misbehaving around the 3 yo mark, independent from how long he slept, so it can be also this developmental leap.