Slow performance for all web traffc

I got my Zscaler solution deployed with GRE and PAC. I noticed that there is a slow performance for all web traffic. What are the possible reasons? Which things to look for and check?

Great that you have deployed Zscaler and setup your tunnels.
First check for your cloud and Zscaler datacenter.

With IPsec and GRE you can have issues with MSS and MTU size that could impact performance. What is the destination you try to reach. You mention PAC files, so you are only forwarding web traffic or do you have full tunnel.

Use to validate your connection and test connection.
Test with just client connector, without tunnel to see if that works well.
Open support ticket if the problem remains.

Best regards,