I had the exact same router for a couple of years.
I did start a thread regarding my dropout connection,after resetting the router and playing with the settings from the configuration pages-i still had problems.
I could not fix the issue,and one particular PCA member suggested the router just got to hot,this i now tend to agree with.
Now a new router (Belkin N series) and all is fine.
Upshot is,in my opinion the firmware update will not solve your issue. I think the G604T has a life of a couple of years and thats it...sorry.
For now and if possible i would reset the router to factory settings if the firmware has not installed.