I have an old Vita spa vintage tub that has 2 problems that I need advice on;

1. I put a new control unit from Spaguts . I also replaced the original 0.75 hp pump with a 1.5 hp and replumbed the inlet with 45 degree fittings to get rid of ay sharp bends in the 1.5" pipe.
I am noticing a lot of cavitation on tjhe inlet . The pump surges ( sucking and blowing). I have tried new filters,, running without filter and still i notice a vortex (tornado effect in the Filter well).
2. The other occurence is my heater trips the panel mounted.GFI breaker even though it is only 6 months old. I ohmed out the heater element and it seems OK 15-20 ohms with no shorts to the outer shell or ground. I know that it is the heater causing the gfi to trip because when I disconnect the heater, the unit runs all day long. My next step is to replace the heater element and see if that fixes thge problem.
Does anyone have any other suggestions or hints to correcting the aforementioned problems? Im really scratching my head over this one.