Trusted Senders are subjected to only SPF/RDNS checks initially, and failing that, are then subjected to all other spam checks. So, this behavior might indicate there is a configuration somewhere causing those initial checks to fail and then resulting in further spam score being associated with the message. Usually that is a gateway that has not been ignored by adding it to Settings>Antispam>IP Bypasses or a malfunctioning DNS server. If you need help tracking this down please submit a ticket with us and we'd be happy to take a look. Have a good one!

Thanks. But if this is the case why does GMAIL work 50% of the time and not the other time? The server averages less than 5% used so I know it's not overwhelmed to timeout. 

That is a great question! To determine the root cause we'd need to review some example messages and review your SMTP and Delivery log files for those delivery sessions.