Sessions drop at random

[brianmahler10]

I have several devices on the inside the firewall that are dropping (ie Xbox Live, Spark im sessions, web sessions to banks, schools, and other as well sessions) from several different computers.  This dropping occurs at random varying from every 15 minutes to much longer.

This is only happening with traffic going thru the firewall.  When I route traffic around the firewall they don't drop.  What logs can I look to to identify why they are dropping?

Thanks.