When an interface is reporting slips from a timing related problem, the T1 clock on the receive wire pair does not match the T1 clock on the transmit wire pair. Even though there are 3 different T1 connections (MLPPP, Phone System, and DMS) there can only be one device providing the timing. All other devices must recover or take timing from the source. This may be tricky because it seems that the MLPPP link is providing timing (as you are set to INTERNAL on T1 0/1) and the DMS appears to be providing timing as well. If the DMS was not providing timing, like Phone System, I believe T1 0/3 would be running clean. That leads us to these questions:
1. Can the DMS clock/receive timing from the ADTRAN?
2. Can the MLPPP clock/receive timing from the ADTRAN?
With the current equipment in place something has to give. If not, there will always be slips.
A drastic measure is to check out a NetVanta 644. It is similar to a TA9XXe unit but can support multiple timing sources: https://supportforums.adtran.com/docs/DOC-4402
Let me know if you have any questions.
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