I pretty much want to know where the PCM, engine and transmissions sensors ground out at. I am getting some really odd stuff happening and want to check all the grounds on this beast as it does have some good signs of aging elsewhere. I am really familiar with the grounding system in my 2000 Bonnie but this 98 Park Ave seems completely different.

Descriptive locations would be a great help, pics would be amazing.

The sensor ground should be above the oil filter under the alternator.

As in the main grounding for the engine sensors?

I also had some trans related codes when I had the engine issues. Any idea where those grounds are located?

Your engine should have 2 grounds. The main ground from the battery, and another one on the back and that'* part of the wiring harness. That one is your sensor ground.