Viscosity is the response of a fluid to certain mechanical forces, whereas heat capacity is purely a function of the amount of energy fed into intermolecular electrostatic interactions. There is likely some role of these intermolecular forces in determining viscosity, but this isn't the whole story. To be honest, I don't think the molecular basis for the viscosity of liquids it very well understood, although someone with a better knowledge of fluid dynamics and rheology may have a better explanation than I could drum up on a whim.