I tested out your shipping rule by creating a new test add to cart page with a display manager on it. When I added an item that was less than 600 it would show the shipping charge. It seems a little off to me though, it is adding the total of the all the items plus 75. If you just wanted to charge 75 then you would use a flat rate and enter 75 for the amount.
It looks like your confirm page would show the shipping charge on it so long as you met the requirements of the rule. The default shopping cart page for PowerStore will not show the shipping regardless, this is as designed.