Better scripting
1. 
Enhanced script editor. Two new functions are added on the script editor toolbar: “Highlight all found” and "Clear Highlights".
2. Upgraded Scripting API. Scripting API is extended to support new relevant UI functionality in scripting.
3. Optimized autocorrelation. Several new autocorrelation rules are added to support a broader range of web applications and frameworks.
4. Test script optimization. If verification determines that there are too many redundant extractors which can be safely deleted, it will prompt you to confirm their deletion. Auto-correlation sometimes creates excess extractors to avoid correlation errors. They should be deleted to reduce resource utilization. 
Scaling Tests
5. 64-bit version. The same installer now sets up 32-bit version or 64 bit version of StresStimulus depending on your system. To determine which version you run, in the StresStimulus About window, check the prefix after StresStimulus version. X86 means 32-bit version and X64 means 64-bit version.
6. Increased Load generator scalability: In the previous versions, some delays between requests were observed on high load levels. In this version, a more optimal thread management algorithm allows to issue requests for a larger number of virtual users without hesitation. As a result, StresStimulus supports a larger number of virtual user emulation with a higher hit rate. Check this page for more about load generator performance.
7. More VU emulation by excluding static resources. Typically static resources such as images and style sheets have very little impact on website performance. In the previous versions you could not exclude them from the test case automatically. In this version you can exclude static resources by default. This allows to emulate a greater number of virtual users with the same hardware resources.
Easier authentication setup
8. Simplified Server authentication configuration. In the previous versions, server credentials had to be entered in every test case. In this version, the same set of credentials is used for all test cases, which simplifies configuration.
9. Host specific credentials. Some web applications use several hosts which require different credentials for authentication. Such authentication schema was not supported in the previous versions. Now you can check the Host-specific Credentials box and for every set of credentials, enter a host to which the credentials will be submitted.
More flexibility in testing Web protocols
10. HTTP vs. HTTPS. Now you can disable the schema change settings for certain test cases. To do so, in the test case property grid, change the parameter Ignore Schema Change to Yes.
11. Timeouts. Now you can disable Timeouts for certain test cases. To do so, in the test case property grid, change the Request Timeout property to Disabled. Use Disabled for determining response times of slow requests.
Better UI
12. Enhanced Test Recent List. If a test from the recent list failed to open because it does not exist, then delete it from the recent list. Also increased the size of the recent test from 15 to 30 items.
13. Easy session comparison. In the session comparison inspector to split the screen 1:1, double-click the vertical separator between Windows or click the Split button on the toolbar.
14. More room for the right panel. To leave more screen real estate to the right panel, click Collapse to the left on the toolbar to maximally shrink the left panel.
15. Keyboard shortcuts for close a test (Ctrl+F4) and Exit Alt+F4
Other Enhancements
16. Parameterizing dynamic file upload. If a dataset contains values representing full paths of existing files, and these values are used to parameterize requests, then instead of including these values in the request, the corresponding files will be uploaded.
17. Automatic installing SSL certificate. In the previous versions, the user needed to install an SSL certificate manually. Now the certificate will be installed automatically by the StresStimulus installer, The SSL certificate is necessary to record test cases using HTTPs protocol.
18. Improved online help searchability. In the previous version you could only search the entire documentation. As a result, too many search results could be returned. In this version, you can narrow down the search to a specific documentation section. For example, you can search just the User Guide, User Interface Reference or Building Test Case section using the search box on the page.
To navigate to other parts of the v4.3 release notes, click the links below:
4.3 is available here