.net 4.0 + w3wp.exe

Recently, we made the jump from .NET 3.5 to .NET 4.0. Now we are seeing a huge performance hit in our web application. The w3wp.exe process is frequently spiking up to 70-80% and staying there for 10+ seconds. Previously, it would only spike up to around 50%, and only then for less than a second for pretty much any of our queries. This has made our app run at about 25% efficiency.

We were previously running .NET 3.5 (32 bit) IIS 6 Windows Server 2008 64bit
and are currently running .NET 4.0 (64 bit) IIS 6 Windows Server 2008 64 bit

Any guidance on how to solve this, or why it would run worse in .NET 4.0 would be much appreciated!
Josh_BladeAsked:
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Josh_BladeAuthor Commented:
After talking with microsoft tech support (after they looked at a dump from our machine), they tell us that due to a change in how memory allocation is handled in 64 bit, a ton of our third party parsing code is now terribly innefficient...

We rolled it back to 32 bit for now, but it looks like we'll have to completely rewrite a huge portion of our app if we ever want to goto 64 bit.
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radcaesarCommented:
This is a broader area to answer.

My suggestion is check your LOG. It may be because of Application Initialization, Bad code/query, Antivirus etc.,

Here are some references to trace where the problem is..........

http://stackoverflow.com/questions/2052633/w3wp-exe-using-100-cpu-where-to-start

http://www.velocityreviews.com/forums/t98410-w3wp-exe-high-cpu-utilization.html

http://forums.iis.net/p/1146821/1875065.aspx
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frankaCommented:
IIS6 on 2008?

any other changes?
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Josh_BladeAuthor Commented:
Actually I typoed, IIS 6 with Windows Server 2003.

The only change between working well and working poorly was going from .NET 3.5 (32) -> .NET 4.0 (64).
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frankaCommented:
is it possible to let it run .NET 32 bit?
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Josh_BladeAuthor Commented:
Talked with MS tech support.
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