Hi @pjred13
MPC555LF4MZP40 is old revision K2.
MPC555LFMZP40 is probably latest revision M but it could be also older K3.
The problem is that mask set version is not explicitly mentioned in the part number in case of these old devices.
Older revision Rev K3 stopped shipping WW19/WW20 2005 (WW stands for work week). Only Rev M is shipped after that (talking about general part numbers, not 'SC...' versions).
In case of doubts, the best way is to read IMMR register to check the PARTNUM and MASKNUM. Then you can compare it with this table:
lukaszadrapa_0-1706686615953.png
All these revisions have different errata lists:
https://www.nxp.com/docs/en/errata/MPC555MCE.pdf
https://www.nxp.com/docs/en/errata/MPC555K3CE.pdf
https://www.nxp.com/docs/en/errata/MPC555K2CE.pdf
If you are going to replace one revision with another, it's necessary to compare the errata and re-validate the product.
Newer revisions fix some errata and there are some minor enhancements, so we can't guarantee that it's 100% compatible replacement.
Regards,
Lukas