In your system profile, edit the sensor configuration for the servlet sensor (or ASP .NET sensor if .NET). There is a table where you can specify which fields in the HTTP request that you'd like to capture. To capture everything, add an entry to capture * from request parameters, another entry to capture * from request attributes, another for * from session attributes, and lastly * from request headers.
Putting the * in the attribute column/value will wildcard and capture all fields from the specified source in the HTTP request.
Keep an eye on the agent overhead.
To see the request values that the sensor is capturing, look at a PurePath and right-click on the servlet node and select "details".
It's a bit late now to help you out, but if anybody stumbles across this forum post, there is an explanation for this issue on this page: