ALDL PCM line length/noise

I'm having problems with my MPVI having connectivity issues with the PCM in my boat and wondering if my ALDL-PCM wire is too long or if corrosion within the wire might be creating noise issues on the bus and precluding connection. The current line is about 10 to 12 feet, the connector is at the helm and PCM back at the transom. This problem has cropped up recently, I changed PCMs thinking that my PCM was bad, it fixed it with the new PCM but now the new PCM is having the same issue. I can read/write both of these PCMs with my bench harness, and I've Ohm'd the wire and it seems fine. Could the line length be an issue with the box?