Volvo Penta Steering Stiff Under Power - Tried New Cable.

[parabellum]

I have a 2006 Striper 26' with a Volvo Penta 5.7 GL-F. At the end of the season the steering started to stiffen up when under power. We had a boat mechanic replace the steering cable and bleed the system to no avail. What I observe is that as I accelerate the motor, the steering gets progressively stiffer. When I check the fluid, there is pressure in the reservoir after shut down and the fluid is foamy. If I turn the wheel to the side, the fluid overflows the reservoir. If I turn the wheel with the engine off, it is easier to turn. I'm thinking something in the lines is plugged but having bled them our mechanic said it should be fine. Any thoughts?