ActiveSync work but not PUSH

Hi all I have problem with this and having difiiculties to explain to Tech
support or find resolution. Here is the story:

When ActiveSync PUSH email is working, it works perfectly fine until the
PUSH portion stops working but the ActiveSync still works. When it is not
working (ActiveSync still work and it will sync but just the push part won't
work, the device would then default to 5 mins pull instead.) Also I noticed
the sync behavior would try to sync, it will complete the first oneand it
will do another two/ three time of sync immediately one after another for no
reason. At this point I know the push email is not working.

I tried to find the server log see if there is any heartbeat error reported
but nothing. I thought my Cisco firewall causing the issue, however, both my
colleagues they were using UTStarcom 6700 TELUS with EVDO have absolutely no
issues at all. My device is K-JAM and is running on GSM carrier, Rogers GPRS
network.

Suspected my device was in faulty stage, I send for repair and they
completely replace the device with new system board (with new IMEI) and
still the problem exist. I then tried to sync with my home Exchange server
and other company's Exchange server, no problem at all. This give me even
more puzzled stage.

If you said it is Exchange issue BUT my the other colleagues can sync and
having push email without problem (with different device); and if you say my
device problem but I can sync with two other server and have push email
without problem. This only leaves me my suspicious that is either my
configuration settings on the dvice screwed up somewhere OR problem with my
network devices and Wireless Carrier.

The quick fix for this is to remote wipe and delete the device, then try
again and hopefully it will work. And if it does, I 'm happy until it fail
again for no reason.

Another of my observation is whenever I try to make changes on the Start>
Settings> Connections, either "Connections" or "Network Cards", it has
potential to screw things up and the push may or may not work but the sync
still work.

I have tried searching the web, looking in to device \Windows\ActiveSync
ctrllog, error codes, read some forums about Wfetch.exe utility, Nextags.exe
and tried log parser... you named it .. I am lost... Am I missing the
obvious? And maybe anyone can point me to what to look for in the ctrl log
or any erro codes?

Remember the key point here is ActiveSync works perfectly fine but the PUSH
email.

Anyone? Thankssss.