Cold sliced and shredded cheese taste different. Have you tried it on a pie yet? If not, you should try that first to see if it still tastes too salty.
Assuming its too salty when used on a pie, adding sugar to your sauce will not make the cheese taste less salty, you will simply have a pizza with sauce that is too sweet AND cheese that is too salty. In this case, I'd suggest using less cheese as a first step.