I'm not able to provide any suggestions based on the information you have provided. Please provide more information if you would like some assistance.
You said the install takes 3-4 hours. Is this a custom DVD? Are you installing with virtual media through an iDRAC? Are you remote or local?
What is slow? Is the CPU maxed out, hard drive slow, network slow, etc? Where is it slow? What testing have you performed? What troubleshooting have you done?
You said the old OS was running fine(2008R2 core). Are you installing 2008R2 again to get a GUI, or is this 2008 32/64?
Dell EMC, Enterprise Engineer
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