Hi Steve,
Something else to consider is the distance between the transom and the front of the hub.
Rule of thumb is between 10 and 13% of the hull length, in your case that would be 90 - 117 mm.
You've chosen to add two large trimtabs, which effectively make the hull longer and narrow the gap between the prop and the transom.
Once a boat pics up speed, a 'dent' in the water forms behind the hull, if the prop is too close to the transom, at some point the prop will stand in that dent, there's less blade surface in the water, the motor can rev out and all you get is a huge roostertail without the matching speed.
If adjusting the stinger doesn't have the desired effect, you may try removing the trimtabs and run the boat to see if that makes a difference.
Apart from the fact most well dialed in hulls don't need trimtabs, it also slows you down...
Regards, Jan.