If there is a Sam's Club that is shorting people hours and paying them partially by cash to compensate, then something is very wrong. It is illegal to simply just short someone's hours and then pay them in cash. You would need to have that money recorded as income, but not taxed. What sort of paystub would they give you with this cash? Or was it treated as a wage advance and then they cashed the wage advance for you? If they did that for the corrected paystub, then that would be OK.

If you don't feel you're being treated fairly though, then leave. I personally try not to leave jobs without a replacement job lined up though myself.