How to find performance hot spots in .Net application?

I have an existing ASP.NET 2.0 web service serves several WinForms clients. In our application, We belive we have performance problem in 开发者_如何学Cseveral levels.

1. Sending toomuch data in syncrounous request
2. Lazy loading, Too many round trip between web service and database
3. POCO <-> Sql object mapping using untyped datasets and reflection[no caching]

This is an existing application with large code base, I would like to instrument this app to find out hotspots.

1. How can I instrument remote apps like winforms client deployed in remote places?
2. How can I instrument Web Service?
3. Edit** Are there any profilers better than VS profiler?
4. Can I trust the profilers to tell me the hot spots, so I don't pollute my code with instrumentation? Or Do I have to take the middle road, profiler + instrumentation?

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This may help:
ASP.NET and WorkerThreads – Interesting performance tweaks
20 Tips to Improve ASP.net Application Performance
Use Custom Http Handlers To Improve Performance in ASP.NET
Best practices for ASP.Net applications
Scaling Strategies for ASP.NET Applications

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I'd recommend checking out dotTrace. I confess I haven't used this, but I've used their other flagship product (Resharper) which is outstanding.

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This is a great tool for profiling and troubleshooting a live web app: http://newrelic.com/