If you have replaced the new tslib (libs+programs) and you still get zeroes, there is still something wrong with the communication between tslib and driver. find out how the driver reports the touch coordinates (with or without MT) and make sure that is how tslib gets its coordinates. I cannot think of anyother reason you are getting zeroes with tslib programs.
I assume here that your driver reads the proper coordinates from ft5x controller. You can verify if it is porperly transfered by vieweing /dev/input/eventX with hexdump.