[JRTJH]

"...and start blending in cold, then it gets too cold. I have to back the cold off until it's barely on."

It almost sounds like the cold valve isn't "tied tightly" to the cold handle/knob. I wonder if the valve is slipping or sloppy when opening/closing and although the handle stays in one position, the "innerds" are still being pushed further opened/closed by the water pressure?

I don't know of anyone who carries Dura faucet replacement parts (valves) so it may be cheaper and less frustrating to replace it rather than try to find parts to repair it.

Then again, changing it out may not solve the problem, the above is only a guess..... Please be sure to let us know what fixed it, if you figure it out.....