Not sure how you are doing sysprep, there are many options, you must be resetting the image somehow that requires a reinstall.
We use sysprep, we are not having this problem.
The best way to do this is simply run the sysprep ONCE (you don't need to do it EACH and every time). You run sysprep PRIOR to creating a template.. that template is now your "golden" image.
Once it's sysprep.. NOW you can install the tools, patches etc.. THEN deploy after that.
That's where you are making your mistake.
Sysprep is to prepare a VM for changing hardware or settings to make it vanilla... Templates are VM's that can be deployed..