PCM, P1694, No Bus Questions

I have reviewed many threads that contain these keywords but have not found one that addresses my issues specifically. I have a 2000 Sport, 4.0, auto... I have an intermittent P1694 code. Sometimes it won't occur for over a month, sometimes it will come on in a few hours. There are no other noticable issues: guages work fine, no other codes, starts and runs just fine, no other lights come on, etc. I have inspected the connectors at the PCM, and those around the transmission. I had originally thought loose battery cables might be spiking the ECM as the marine terminals kept loosening up on me. I have since switched to nylock nuts and everything is tight there. I have not changed the CPS as that sensor seems to be related to the guage problems people have. I did take it to the dealer and he said his scanner was connecting just fine to both the PCM and Aisin tranny module (which I assume is the one under the dash on the trans hump). I have also checked the PCM connectors and added dielectric grease. My next step is a new ECM (which I have). The "instructions" say a scantool of some kind is needed to link the new computer with the existing modules/sensors. This makes no sense to me as it was reflashed to the specs of my jeep (or so I assume as they had to have my VIN).

Anyone have any thoughts?

the PCMs just switch out......nothing needs to be changed in any "settings"

UPDATE: Spent the day working on this thing. I installed the new (reman) ECM and the 1694 code came back after 20 miles of driving - still no other signs of a problem, just the light. I put the stock ECM back in. I then started inspecting wires. I found a ground that had the insulation rubbed through but that was it for underhood. I then pulled the dash and inspected the wiring harnesses inside (and to better assess where water is leaking into the cab but that is another issue for another day) and the only thing of any note was that the trans module was a little loose but the wires were tight. I got underneath and checked the harness connector for the CPS and added dielectric grease. My biggest oops of the day was disassembling and inspecting one of the plugs to the ECM. Took a couple hours to get it reassembled and then to find I put it back upside down... When it wouldn't start I uttered a few choice words before discovering the error. I fixed that issue and it runs now, but it was too late to find out what trouble codes I created due to the aforementioned error and to see if the original code reappeared.

Since I have become fairly adept at checking the ECM plugs now, can anyone confirm which plug links with the trans module? I checked the middle white one as I thought that was the one I had seen referenced elsewhere on the site.

Also, where do the wires from the ECM meet the transmission? I don't think I have checked this connection.

Any help is appreciated.

Thanks