Steve,

The system does use fuel trims and it will be available from your scanner. Maybe you are having trouble identifying the block data.

What are you using to measure the signals? You need to measure the lambda signal and the ground. Live data is not good enough in a case like this.
If the Lambda signal is actually doing what you have seen it do in live data then that is not right and this is what you should test before you go any further.

If the ground voltage is going high you could add another ground to it. This could even be an ECU fault.