You are describing a common problem with low head speed helicopters.
Two common fixes to this are head stiffeners and higher head speed.
The advantage of Head Stiffeners, which reduce coning, is often argued. I have used this myself, and I think that it did help some.
Higher head speed is clearly effective in reducing the pitch up/forward flight problem. I have experimented with this and it makes a big difference.
So, consider cutting down your blades and putting on a bigger pinion.