Anyone have this issue?

Here's what's happening. I get everything set to surf. Ballast full, ZeroOff set, etc. Hit the throttle and once up to speed, the engine starts reving up and down, and speed on the dash screen starts cycling up and down by about 1mph.

Here's where it gets interesting. If I back the throttle off the engine stops surging but the speed in the dash keeps cycling up and down even though my speed is consistent.

Only thing I found to fix it is to turn off the engine and cycle the battery.

Bad GPS unit? I'm super confused.