I am simulating a 4 layer PCB but need to show a visible plot of the return current for various frequencies. I need to show results based on issues with the return currents.
What is the wavelength compared to the thickness of the layers? This is an important factor in deciding which solver to use. It sounds like you are working at VHF or below and the board will be 1/1000 wavelength thick. I do not think the TLM solver will be good for that.