3.0 = 5hp19, 4.2 = 5hp24, is why you receive that message.
if you used the original 3.0 gearbox/tcu, this can be fixed in the 4.2 ecu software very easily.
if you used the original 4.2 gearbox, then you should be using 4.2 tcu as well.
I used the original 3.0 transmission ( 5HP19 ) and ECU. I could not find the solution anywhere I looked, right now I am trying a different TCU from a 2.7t but if you have a solution it would be great. The error message was 18249 - Engine Control Module / Transmission Control Module Incompatible