Thanks Lyndel. Unfortunately, Serial.M is on Extender 1, Port 4. Serial.M88 is on Extender 6, Port 1. The link you sent was very helpful though and I certainly plan to move a few things around this weekend (1-way stuff on ports 3 & 4 with 2-way on Ports 1 & 2). That is not the case today.

If you can think of anything else that may be causing the issue above, please let me know. Thanks again.