Is there a way that I can properly troubleshoot if I have a LEC issue or dropped packets from a 2421 or ATA?

I have issues terminating many faxes from 2421's. I almost never get ATA to send fax properly. This is,I think that config is right as sometimes they go through, sometimes they don't. For the longest time I thought it was dropped packets across the WLAN, but know I see that even on great links with no bandwidth being consumed, their are certain numbers that always fail! Thought it may be the PRIs interaction with the gateway/ccm or remote 2421....