When troubleshooting memory related issues you will run GCRoot against objects in a given MethodTable. The process of GCRoot'ing each of the objects individually to chase down a root can be hit and miss. Use the command below to run GCRoot against a given MethodTable. The result will be the output of !GCRoot for each object. Happy hunting!
.foreach (obj {!dumpheap -short -mt 0x000123ab}) {!gcroot obj}