Stiff steering

[Spoff4]

Our power catamaran has developed an odd steering issue . At stop or anything below about 7 knots, the steering is normal. The wheel turns freely lock to lock. However, above 7 knots, and especially above 12 knots, the steering is extremely stiff. It's a hydraulic system and it's a cat, so there are two rudders. There is no play in the rudder posts and there is nothing fouled on the rudders.
The rudders were toed in about 15 degrees and we have corrected that. I am skeptical that having the rudders out of alignment by 15 degrees would make the steering as stiff as it was. Before we relaunch and test the steering, I thought I'd see if anyone has any thoughts as to what else could cause the stiff steering.
Any thoughts?
Thanks.
-Spoff4