M.F.
Maybe it's not a matter of losing the nap, but maybe shortening it or making sure he gets up by a certain time in the afternoon. We discovered that we needed them up by 3:30 at the latest to get them to sleep through the night, and as they age, we reduced their nap to and hour and then to every other day. Also consider when you are putting him to sleep... and adjust a little later. Have you tried music or a noise machine?