What should and can I do to test my BCM?

What is your question?

The gear doesn't work (P,R,N,D,3,L) all of them are lit up vs only one and after resetting the computer (disconnect the battery for a few mins) everything works as normal but the first thing that cuts out is the gears, then after a couple days the entire cluster dies ( all gauges read 0 and no bus is seen as mileage) all the while the car runs like nothing is wrong. The codes I get are random but P 1698 is almost always there which points to the TCM. BUT as I drive, sometimes my interior lights come on randomly and shut off shortly, which points to the BCM.