Sounds like a familar tune; Client calls the help desk and complains that 'everything is slow'.
The network folks check the client switch port and find no errors. They access the same application/server with no issues. Then the IT folks comment how this guys is always calling him and it must be just him.
I overheard this and asked if I can help since I'm there already. They give me the 30 second review as to what they did and what they found. I explained that I could find fault in anything they did and agree that things look just fine.
Then I ask if anyone has physicaly gone over to check things out, to which they replied, "Nope". I then suggest we go for 'a walk' to further investiagte. In this case the client was only one floor down, so goign over wasnt a big time waster.
When we got there we double checked everything we checked before and validated which port, switch, vlan and client IP. Then I checked the Advanced -> Bindings configuration and noticed that the LAN adapter was second and should be first. I simply rearranged the bindings and everything sped up and the client was happy.
The customer went back and found that the bindings order we found was a default in their 'standard build or image' and are taking steps to push the required changes across the board.