Fin Issue?

I recently made a board with the following dimensions: 7’10" x 15.5" x 24" x 16" x 3". Rocker is 5" in the nose and 2.5" in the tail. I am using a single fin. The board catches waves great. Initally the board flies and then dies or stalls out in the wave. Also the nose seems to want to go straight down. Just wondering if I added side fins, would this fix the problem? Also what brand of boxes would be suggested to install on an already finished board? Any help or suggestions would be appreciated. Thanks

side fins could help drive the board with a little pump better than a single. get ProBox Hawaii fin boxes. they’re installed after the hotcoat, and they’re great.