We are seeing really slow response times and found there are slow third party content which is causing in slow response times. These each third party content is showing like number of resources it is having. Is it possible to do deeper analysis on this and see what exactly those resources are?
For third party calls you are either waiting for an internal service or application (web call that has a return) or external service for some sort content/value. Since these don't have Dynatrace agents on them you won't be able to get a detailed breakdown of how the time is spent to fulfill those calls. In the case of the internal third party service you may be able to instrument that application with Dynatrace and then the purepath will follow into that application, the only "gotcha" here is that they must belong to the same system profile otherwise the call from application A will be the entry point for applicaion B, but applicaion A will still show the same amount of info.
Have you tried using the "Third Party Hotspot" BT to do some troubleshooting?
After you narrow it down to some specific third parties, you could create some "Third party content count" and "Third party content load time" measures to help you zoom in on the specific "Resource types" (Images, Scripts, Stylesheets, Other resources, or Custom resources) that are the biggest contributors to narrow it down further.