muddy gradient

You can add a second fill under this one to fill in the muddiness. 

Set the top fill to multiply, and set the second fill as a gradient from white to the lighter blue and back to white. Adjust the stops until you get the appearance you want.  

Top is your gradient alone - bottom is with the added gradient fill.

How does it look with Overprint Preview On?

You need to add a third color where the gradients blend. This is a commonly known perceptive issue because in blending the colors the luminance drops at certain points, making the colors look dull. That's why at the point you should insert a relatively bright color that is somewhere in the middle of your existing ones.

Mylenium

Pantone spot colors? Or Pantone CMYK versions?