OKAY! I think I have finally got it stable!
For my 8120 I am using a Linksys WRT110 router.
I am only using G wireless mode on channel 3
I am not broadcasting my SSID
I am using WPA2 Personal security AES encryption
I am using MAC filtering
AP Isolation is enabled. (Not sure if this is helping)
Beacon Interval 100 (mine would never connect with it at 50)
DTIM interval 2
Fragmentation threshold 2304
RTS threshold 2304
Battery rebooted 8120 many times.
As near as I can tell, (havenít been staring at device constantly) i have had UMA stable for 2 hours... (thatís a feat for me)
I will recap again tomorrow and see how it behaves.