Thanks for the replies, Cape X5 and Slick GT1. I will have to check production dates to see if there has been any revision. I may have to ring out the individual wires from the TCM to the temp sensor. I thought I had that by changing out the entire harness. The perplexing thing is the delay in the fault code returning after driving for that time/distance after swapping the entire harness. I ran normally for quite a while before reverting to the failed state, with same code.
I won't let this thing beat me!