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Call a Lexus dealer and ask for the part number for your ECU, and to see if a number supersedes your current one. Then compare the number of your replacement ECU, it needs to either match the original exactly, or match the supersedes part.
Using a different part number can have unintended results.
Supersede means a new number (the part itself may be revised/improved) replaces an old one, and that the new part is 100% compatible with the original.