ZOMBIE Call detection drops mid sentence

Hi,

Some background first:

freepbx 2.11 about 170 SIP stations
SIP trunk to provider with a router on local VOICE network as a route to their voice controller.
SIp trunk to another custom asterisk on same network for dialer application
No NAT that I’m aware of, maybe on the provider side somewhere down the line?

The problem comes in that random calls drop mid sentence and we get a line like this in reporting:
Time | Event | CNAM | CNUM | ANI | DID | AMA | exten | context | App | channel | UserDefType | EventExtra | CEL Table
2015-04-20 13:31:31 | CHAN_START | Gibraham Chavez | 177 | | | DEFAULT | 17736911990 | from-internal | | SIP/177-00059833 | | | |
2015-04-20 13:31:31 | CHAN_START | | | | | DEFAULT | s | from-trunk | | SIP/2242578404-00059834 | | | |
2015-04-20 13:31:41 | ANSWER | CID:8478279740 | 17736911990 | | | DEFAULT | 17736911990 | from-trunk | AppDial | SIP/2242578404-00059834 | | | |
2015-04-20 13:31:41 | ANSWER | Americash LLC | 8478279740 | 177 | 17736911990 | DEFAULT | s | macro-dialout-trunk | Dial | SIP/177-00059833 | | | |
2015-04-20 13:31:41 | BRIDGE_START | Americash LLC | 8478279740 | 177 | 17736911990 | DEFAULT | s | macro-dialout-trunk | Dial | SIP/177-00059833 | | | |
2015-04-20 13:33:31 | CHAN_START | | | | | DEFAULT | s | from-trunk | | AsyncGoto/SIP/2242578404-00059834 | | | |
2015-04-20 13:33:31 | HANGUP | CID:8478279740 | 17736911990 | | | DEFAULT | h | from-trunk | | SIP/2242578404-00059834 | | | |
2015-04-20 13:33:31 | CHAN_END | CID:8478279740 | 17736911990 | | | DEFAULT | h | from-trunk | | SIP/2242578404-00059834 | | | |
2015-04-20 13:33:31 | HANGUP | | | | | DEFAULT | | macro-dialout-trunk | AppDial | AsyncGoto/SIP/2242578404-00059834 | | | |
2015-04-20 13:33:31 | CHAN_END | | | | | DEFAULT | | macro-dialout-trunk | AppDial | AsyncGoto/SIP/2242578404-00059834 | | | |
2015-04-20 13:33:31 | HANGUP | Americash LLC | 8478279740 | 177 | 17736911990 | DEFAULT | 17736911990 | from-internal | | SIP/177-00059833 | | | |
2015-04-20 13:33:31 | CHAN_END | Americash LLC | 8478279740 | 177 | 17736911990 | DEFAULT | 17736911990 | from-internal | | SIP/177-00059833 | | | |
2015-04-20 13:33:31 | LINKEDID_END | Americash LLC | 8478279740 | 177 | 17736911990 | DEFAULT | 17736911990 | from-internal | | SIP/177-00059833

Hope that shows up ok. The problem is very sporadic and some will never see it and others will see it 2-3 times a day. Anyone have any avenues to explore? Here is my trunk config just as a start since more information will likely be needed:

fromdomain=10.16.66.2
host=10.250.0.5
qualify=yes
dtmfmode=auto
secret=11223344
type=peer
username=2242578404
allow=ulaw
canreinvite=no
context=from-trunk
directmedia=no
insecure=invite
relaxdtmf=no

Any help will be greatly appreciated.

Rafal