TFS Web Access very slow using IE

Hi

We are experiencing very slow responses updating Workitems via Web Access using IE.  We're running TFS 2013.4.  Tested using IE 9 & 11, no significant difference.  Bypassed proxy, again no difference.  No issues when using Chrome. Interestingly we don't experience the same lag across all workitems, but there appears to be no correlation between workitem links, attachments etc. and speed.   We're at a loss to explain this!  Any advice would be greatly appreciated.

Thanks

Rob