IIS WCF requests slow-FREB and Debugdiag logs available

I'm trying to troubleshoot slow performance for some IIS requests.

Server 2012  - IIS8

CLR version = 4.6.1639.0

I captured FREB logs and got some process dumps. We have some requests that take >30 secs. The Freb logs are all the same. All of the time taken is here in AspNetpipelineLeave. I'm having trouble understanding whats going on here. The Debugdiag reports just have Warning about threads waiting for .net garbage collection - 29.51% of threads blocked (18 threads). Any guidance would be appreciated. Thanks.

<div class="duration">35085 ms</div>

<div id="section_detail_36_details"></div> <div> <div class="duration"></div> <div class="severity-verbose">Verbose</div>36. -AspNetPipelineLeave<div id="section_detail_36_details">

ConnID	0
Context ID	{00000000-0000-0000-85DF-0080010000F5}
Data1	System.ServiceModel.Activation.ServiceHttpModule

</div> </div>

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