What kind of tech support is this? Since these guys are only being paid around $19 per hour, I'm going to assume we're not talking enterprise/isp-level multiple router lab setups using BGP, OSPF, 802.1q, blah blah blah...? This makes a difference because of the difference in quality/maturity of the personnel you're hiring.
Employee performance must be based on more than simple call volume and % resolution/customer satisfaction. Every call is different; they can range from "how do i.." to "help! My network is down!" It would be easy for someone to pad their caseload with easy calls.
You don't specify what relationship you have with your employees; are you their direct supervisor, or are you higher up the food chain with no direct contact with members of the department? Their supervisor needs to be in constant communication with them, going over workload, problems, solutions, training, expectations, performance. Employees who do not perform can be weeded out, and if it's understood that certain forms of game playing are forbidden, employees who violate this rule can be dropped.