if running 4.1 make sure HTTP Layer 7 optimization is enabled
show accelerator HTTP
Through GUI, click on device and check configuration / acceleration enabled features. Also check the report time, over last day, last hour, etc.
Just an FYI but there is a bug associated with 4.1.1c and the HTTP accelerator.
CSCsv69306-Under certain conditions, HTTP clients whose connections are being optimized by HTTP accelerator can experience slow response.
I had to disable the HTTP accelerator for all my devices but I am now running 4.1.1d and it is enabled.