Take a look at JMeter Functions like:
- __Random() - which generates a random number in the given range
- __RandomString() - which generates a random string from the given input
- __threadNum() - which returns the current thread number
- __UUID() - which returns an unique GUID structure
- __time() - which returns current time stamp in different formats
- any combination of above
JMeter functions can be used anywhere in the test so you can put them directly into your request body.
Some more recommendations:
- Don't use JMeter GUI for running the load test, GUI mode is designed for tests development and debugging only, the tests themselves need to be run in command-line non-GUI mode
- Remove all the listeners from the test plan while running your load test as JMeter listeners are very resource intensive and create unnecessary overhead.