.NET Performance Optimization Needed

I already have the full source code for a desktop .NET application and I’m happy with its functionality, but it feels sluggish. What I’m looking for is a focused performance pass aimed purely at speed—no new features or bug-hunting, just making the existing code run faster. Right now the two problem spots are:

• Data-intensive routines that slow to a crawl when large datasets are loaded or complex calculations run.
• User-interface lag; controls hesitate and redraw slowly while those same heavy operations are happening.

You’re free to suggest profiling tools such as Visual Studio Profiler, dotTrace, or PerfView; whatever pinpoints bottlenecks most effectively. Once identified, I’d like you to refactor the hotspots—algorithm tweaks, async/await, caching, or any other proven techniques that trim execution time without breaking current behavior.

Deliverables
• Optimised solution/project files ready to build
• Brief change log outlining the key optimisations and measured speed gains
• Any scripts or settings used for profiling so I can reproduce the results

I’ll provide the code and a sample dataset immediately after we agree on the engagement.