You use the supplied 26cm Drake Natural, right? I think something like a 26cm Drake crossover would help. It has a fair bit more power than the Natural 26 despite not being deeper. In particular, there is more drive lower down in the fins which would help. I think that with this fin, you could also drive the board a little harder over the the fin which I actually will help over the chop. You will off course still need to be responsive when you hit chop, but it helps when you can rely on the fin to "connect" to the water in a solid way after a small air passage.
You could go for the crossover 28 too, but I think that will be too much fin for a 5.0 even for your weight.
How is the PA 86 in the same conditions? Which fin do you use on that one?