If it helps, when I transitioned my DS1 to one nap, I did it quite slowly at first. I did a long am nap and a short pm, and I just moved the morning nap later by 15 mins every week. Then one week, we were just doing something and he was still zipping around at 11:30am, so I fed him lunch and he was asleep by noon. After that, it was no problem getting him to stay awake for another 30 minutes, then 45. The one thing that REALLY messed our LO, but works for others, was moving his BT around. We tried to put him to bed early on days when he had a short mid-day nap but that just messed him up because my children like their routines. Once we stuck with his usual bedtime, come hell or high water, he was totally fine.