Why won't my custom shipping rate work for larger orders?

I tried making a custom shipping rate for the members state, but it still did not work. He could purchase 53 cards, but could not buy 54. I think the issue is with the shipping rate, and it increases to the next pricing category, but we are talking about a 8 ounce package, vs a bit more pushing it up. What solutions are there? This has happened before, but not frequent.